KR100384016B1 - High durable Pd-Rh three way catalyst for NOx reduction - Google Patents

Abstract

The present invention relates to a palladium-rhodium tertiary catalyst for removing nitrogen oxides and a method of manufacturing the same, and more particularly, to a palladium-rhodium tertiary catalyst containing only bulk cerium oxide (CeO ₂ ) as a cerium compound, a bulk cerium oxide ( In addition to CeO ₂ ), it contains cerium-zirconium composite oxide [(Ce.Zr) O ₂ ] at the same time, which improves heat resistance, and it contains excellent Praseodymic oxide (PrO ₂ ) to purify the exhaust gas. The present invention relates to an improved palladium-rhodium tertiary catalyst which is excellent as a catalyst for purifying gas in automobile exhaust gas or various industrial facilities due to its excellent removal effect of nitrogen oxide (NO _X ) and a method for producing the same.

Description

Palladium-rhodium three-way catalyst for nitrogen oxide removal and its manufacturing method {High durable Pd-Rh three way catalyst for NOx reduction}

The present invention relates to a palladium-rhodium tertiary catalyst for removing nitrogen oxides and a method of manufacturing the same, and more particularly, to a palladium-rhodium tertiary catalyst containing only bulk cerium oxide (CeO ₂ ) as a cerium compound, a bulk cerium oxide ( In addition to CeO ₂ ), it contains cerium-zirconium composite oxide [(Ce.Zr) O ₂ ] at the same time, which improves heat resistance, and it contains excellent Praseodymic oxide (PrO ₂ ) to purify the exhaust gas. The present invention relates to an improved palladium-rhodium tertiary catalyst which is excellent as a catalyst for purifying gas in automobile exhaust gas or various industrial facilities due to its excellent removal effect of nitrogen oxide (NO _X ) and a method for producing the same.

In general, nitrogen oxides (NO _X ) contained in exhaust gases emitted from various industrial facilities or automobile exhaust gases refer to nitrogen monoxide, nitrogen dioxide, and nitrous oxide, which cause air pollution such as other carbon oxides and sulfur oxides. One of the representative materials. Of these, nitrous oxide is not toxic, but it is a major source of global warming along with carbon dioxide. Nitrogen monoxide is a major component of exhaust gas nitrogen oxides and is easily converted to nitrogen dioxide by reacting with oxygen at room temperature when released into the air. In particular, nitrogen monoxide and nitrogen dioxide are carcinogenic substances that are very harmful to the human body, causing serious air pollution, and together with sulfur oxides, are causing acid rain. The emissions of these nitrogen oxides are mainly due to the reaction of nitrogen and oxygen in the air and the combustion of nitrogen compounds contained in the fuel at high temperature, except for industrial waste. Therefore, in addition to the method of reducing the production of nitrogen oxides through the combustion control, the development of nitrogen oxide removal technology by the exhaust gas treatment is inevitable.

Nitrogen oxide removal technology is largely divided into the case of using a catalyst and the case of treatment without using a catalyst. When a catalyst is used, it is divided into a method of using a reducing agent and a method of directly decomposing on a catalyst without a reducing agent. In the case where a catalyst and a reducing agent are used together, the treatment technology using ammonia as a reducing agent has been commercialized for the first time in the early 1980s, and its use has rapidly increased. However, the method of using the ammonia as a reducing agent has a problem of causing secondary pollution in which unreacted ammonia is discharged into the air, in addition to the disadvantage that the equipment cost is high due to the difficulty of transporting and charging the ammonia and the corrosiveness of the ammonia.

On the other hand, since the 1970s, much effort has been focused on research on platinum group metals or metal oxide catalysts in order to directly decompose nitrogen monoxide or to develop a reduction catalyst using a selective catalytic reducing agent. Particularly, for automobile exhaust gas, when the air-fuel ratio of the vehicle is stoichiometric, the platinum-palladium-rhodium tertiary catalyst, which is a catalyst for converting the exhaust gas, converts carbon monoxide, hydrocarbons, and nitrogen oxides, which are exhaust gas pollutants, into almost 90% or more harmless gas. It has been reported to have a converting effect.

The three way catalyst used to remove pollutants such as nitrogen oxides refers to a catalyst that reacts with hydrocarbon-based compounds, carbon monoxide and nitrogen oxides (NOx), which are harmful components of exhaust gas, to remove these compounds. Pt / Rh, Pd / Rh or Pt / Pd / Rh based ternary catalysts have been used.

Recently, palladium ternary catalysts using only palladium (Pd) without rhodium (Rh) have been developed and known [Korean Patent No. 235029, US Patent No. 6,043,188], and the manufacturing method thereof is as follows.

That is, the palladium solution is impregnated with alumina and then reduced, and then, cerium oxide and mixed solution are added thereto, and then the pH is adjusted and reacted and milled to obtain a coating slurry of the catalyst material, followed by ceramic monolith. Immersion, coating, drying and calcining to prepare a palladium tertiary catalyst.

However, these three-way catalysts have some effect on the removal of harmful gases such as nitrogen oxides, but the heat resistance is somewhat lowered and there is room for further improvement in the purification effect. In particular, nitrogen oxides are known to be thermostable in the low temperature range compared to nitrogen and oxygen, so it is best to directly decompose nitrogen oxides in the exhaust gas on the catalyst and convert them to nitrogen and oxygen, but it requires high temperature reaction temperature. Due to the problem that the catalyst activity is easily lowered, so far no improved catalyst has been developed that can be put into practical use.

In addition, the use of Zr-Ce complex oxide as a Pd / Rh-based three-way catalyst improves oxygen storage capacity and improves heat resistance. However, many studies have been published. There was an inferior problem in terms of high heat resistance.

Meanwhile, advanced countries continue to strictly regulate various pollutant emissions, and the demand for exhaust gas purification technology is expected to increase significantly. Therefore, it remains a problem to develop a three-way catalyst having better nitrogen oxide removal ability and heat resistance than the conventional one, and to effectively use it.

Thus, the present inventors prior art for the purpose of practical use of the three-way catalyst improve the NOx Removal and research efforts result in order to increase the heat resistance, a bulk cerium (CeO _2), and the cerium separately oxide-zirconium composite oxide [(Ce and Zr) The use of O ₂ ] together with the addition of praseodymium oxide (PrO ₂ ) has been found to be capable of removing nitrogen oxide with high efficiency and improved heat resistance at the same time as compared with the conventional art, thereby completing the present invention.

Therefore, the present invention adds a new component that has not been conventionally used in the palladium-rhodium ternary catalyst to improve the exhaust gas purification effect while improving heat resistance and the like, and particularly the palladium-rhodium especially the nitrogen oxide purification effect is improved. The purpose is to provide a three-way catalyst.

In the present invention, in the palladium-rhodium ternary catalyst coated with a ceramic monolith carrier, palladium, rhodium and cerium components,

Based on 100 parts by weight of alumina per unit volume of the total carrier apparent volume, a component containing 5 to 10 parts by weight of cerium oxide, 18 to 27 parts by weight of cerium-zirconium compound oxide, and 3 to 10 parts by weight of praseodymium oxide is coated. It is characterized by the palladium-rhodium ternary catalyst for nitrogen oxide removal.

In addition, the present invention is a method of producing a palladium tertiary catalyst by impregnating a palladium solution in alumina and reacting with a supported component containing cerium oxide after reduction to obtain a catalyst slurry, and coating the catalyst slurry on a ceramic monolith carrier,

1 to 5 parts by weight of palladium and 0.1 to 1 parts by weight of rhodium are impregnated into alumina based on 100 parts by weight of alumina per unit volume of the total carrier apparent volume, and then 5 to 10 parts by weight of cerium oxide and a cerium-zirconium compound oxide 18 to 27 It is characterized by producing a palladium-rhodium tertiary catalyst by adding by weight, reacting 3 to 10 parts by weight of praseodymium oxide, 5 to 6 parts by weight of barium oxide and 1 to 2 parts by weight of lanthanum oxide.

The present invention will be described in more detail as follows.

The present invention relates to a palladium-rhodium ternary catalyst having an excellent purifying effect of automobile exhaust gas, among other things, an excellent effect of removing nitrogen oxides and improved heat resistance, and a method of manufacturing the same.

The method for preparing a palladium-rhodium tertiary catalyst for removing nitrogen oxides according to the present invention will be described in more detail as follows.

In a first process, a palladium solution and a rhodium solution are impregnated into alumina (Al ₂ O ₃ ), and then a process of reducing it is performed. At this time, the palladium is added 1 to 5 parts by weight based on 100 parts by weight of alumina, the rhodium is added to 0.1 to 1 parts by weight. In addition, the reduction method is added dropwise so that the hydrazine hydride (hydrazinehydrate) is 1.5 to 20 ml per 1 g of palladium.

In the second process, bulk cerium oxide (CeO ₂ ) and cerium-zirconium composite oxide [(Ce.Zr) O ₂ ] are added, and praseodymium oxide (PrO ₂ ) is added, followed by addition of a mixed solution. To perform the process.

At this time, the reason for using CeO ₂ and (Ce.Zr) O ₂ simultaneously is to induce structural stabilization and to improve heat resistance. In addition, since the (Ce.Zr) O ₂ is used in an amount of 18 to 27 parts by weight, it is difficult to expect improvement in heat resistance when used in a small amount, and when used too much, it is not only economical but also a possibility of deterioration in physical properties. The PrO ₂ effectively removes nitrogen oxides by controlling CO adsorption and oxygen storage capacity by stabilizing Ce on a catalyst. At this time, 3 to 10 parts by weight of PrO ₂ is used with respect to 100 parts by weight of the alumina component. When using less than 3 parts by weight, there is a problem that the effect of improving heat resistance and improving the efficiency of purifying nitrogen oxides decreases. There is a problem that the price increases compared to the effect.

The mixed solution is a mixture of barium oxide, lanthanum oxide, acetic acid and water, and 5 to 6 parts by weight of barium oxide and 1 to 2 parts by weight of lanthanum oxide are preferably added to improve the heat resistance of alumina and the properties of cerium oxide. Do. In addition, it is preferable to use 23.5-33.5 parts by weight of acetic acid for adjusting the pH, and the pH is preferably 4.5 or less for controlling the viscosity in preparing the catalyst slurry for the next coating.

In a third process, the mixture is milled by controlling the slurry reaction and particle size by a ball mill method to have a particle size of 1 to 7 μm to 90% or more of all the particles. In this case, there is a problem that the purification efficiency and durability is reduced when milling the particle size outside the above range. As a result of the milling process, a catalyst slurry having a solid content of 35 to 45% and a viscosity of 250 to 400 cpsi is obtained.

In a fourth process, the ceramic monolith carrier is immersed in the catalyst slurry, coated, dried and calcined. The coating of the present invention is a single coating using a segregation effect, which is generally a double coating to place any component in a desired position, but using a compound state having the property of agglomeration with each other By locating the components in the required portion can maximize the efficiency of the single coating, it is an effect that can improve the catalytic performance. In other words, in the coating of the present invention, the desired component, which can be in the form of dipping, is coated at a desired position by the method of adding each component and selecting an appropriate starting material of the component. In addition, the drying is carried out for 2 hours at 150 ℃ temperature in a drying furnace, firing is carried out for 4 hours at 450 ~ 550 ℃ temperature 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 and harmful compounds are formed in the coating layer.

Therefore, the palladium-rhodium tertiary catalyst for removing nitrogen oxides according to the present invention as described above is excellent in heat resistance and nitrogen oxide removal ability, which can be widely applied to the field of single layer coating catalyst, and is useful for automobile exhaust gas purification, diesel catalyst and industrial catalyst. Can be used.

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

Example

It is carried out by the method described below, the specific amount of each component is shown in Table 1 below. The solution containing palladium and rhodium was impregnated in alumina and then reduced by dropwise addition of hydrazine hydrate to 1.66 ml per g of palladium. Then, CeO ₂ and (Ce.Zr) O ₂ were mixed and added, and PrO ₂ was added. Further, a solution containing barium oxide, lanthanum oxide, acetic acid and water was added thereto, and the pH was adjusted to 4.2 using acetic acid. It was. In addition, a catalyst slurry having a solid content of 40% and a viscosity of 300 cpsi was obtained by milling the particles having a particle size of 1 to 7 μm to 90% of all particles by a ball mill method. The ceramic monolith carrier was immersed and coated therein, dried at 150 ° C. for 2 hours in a drying furnace and calcined at 450-550 ° C. in an electric furnace for 4 hours.

Comparative Example 1

Prepared in the same manner as in Example 1, but was carried out in the composition shown in Table 1 without using rhodium.

Comparative Example 2

The Pd-Rh-based three-way catalyst was prepared by a known method, but was performed in the composition shown in Table 1 below.

Thereafter, the catalyst prepared according to Examples and Comparative Examples 1 and 2 was compared and the results are shown in Table 2 below.

In Table 2, the low temperature active temperature is a 50% purification temperature, the lower the measured temperature means that the purification efficiency of hydrocarbons, carbon monoxide, nitrogen oxides is excellent. According to the results of Table 2, in the case of the example of the three-way catalyst of the present invention, the removal effect of NO _X measured after 950 ° C. after aging at 950 ° C. after aging at 950 ° C. was maintained as compared with Comparative Examples 1 to 2. It was confirmed that the nitrogen oxide removal effect is excellent and the heat resistance is improved.

As described above, the palladium-rhodium tertiary catalyst of the present invention improves the nitrogen oxide removal ability of the catalyst by greatly adjusting the adsorption and oxygen storage capacity of carbon monoxide on the catalyst by the newly contained praseodymidite, and the bulk cerium oxide and cerium -By using zirconium complex oxide at the same time, heat resistance can be strengthened compared to the existing catalyst containing only bulk cerium oxide, so that it can be widely utilized as various purification catalysts and industrial catalysts.

Claims (2)

In the palladium-rhodium three-way catalyst coated with a ceramic monolith carrier palladium, rhodium and cerium components, Coated with a component containing 5 to 10 parts by weight of cerium oxide, 18 to 27 parts by weight of cerium-zirconium compound oxide, and 3 to 10 parts by weight of praseodymium oxide, based on 100 parts by weight of alumina per unit volume based on the total carrier apparent volume. Palladium-rhodium three-way catalyst for removing nitrogen oxides, characterized in that. In the method of preparing a palladium tertiary catalyst by impregnating a palladium solution into alumina and reacting with a supported component containing cerium oxide after reduction, coating the catalyst slurry on a ceramic monolith carrier, 1 to 5 parts by weight of palladium and 0.1 to 1 parts by weight of rhodium are impregnated into alumina based on 100 parts by weight of alumina per unit volume of the total carrier apparent volume, and then 5 to 10 parts by weight of cerium oxide and a cerium-zirconium compound oxide 18 to 27 A method for producing a palladium-rhodium tertiary catalyst characterized by adding a weight part, 3 to 10 parts by weight of praseodymium oxide, 5 to 6 parts by weight of barium oxide, and 1 to 2 parts by weight of lanthanum oxide.