KR101336595B1 - A catalyst for purifying exhaust gas with bimodal size distribution of supports - Google Patents

Abstract

The present invention is for purifying exhaust gas in which the distribution of support particles for supporting a noble metal component, which is composed of a first support of relatively large particles and a second support of relatively small particles, is in a bimodal form. The present invention relates to a catalyst composition, which has excellent low temperature activity and can achieve deNOx improvement in a high-speed running section compared to a catalyst for purifying exhaust gas.

Description

A catalyst for purifying exhaust gas with bimodal size distribution of supports}

The present invention relates to a catalyst for purifying exhaust gas of an internal combustion engine, more particularly, a catalyst for purifying exhaust gas having bimodal distribution particle size supports, in a catalyst of the type commonly referred to as 'three-way conversion' catalyst.

Three-way conversion catalysts ('TWC') have utility in many fields, including reducing nitrogen oxide (NOx), carbon monoxide (CO) and hydrocarbon (HC) pollutants from internal combustion engines such as automobiles and other gasoline fuel engines. Three-way conversion catalysts include oxidation of HC and CO; It is ployfunctional in that it can catalyze NOx reduction substantially simultaneously. In most countries, emission standards for NOx, CO and unburned HC pollutants are established, and new vehicles must meet these standards. To meet this criterion, a catalytic converter comprising a TWC catalyst is placed in the exhaust line of the internal combustion engine. The catalyst promotes unburned HC and CO oxidation, and NOx reduction by oxygen. For example, NOx reduction is relatively advantageous by storing oxygen during lean (relatively low fuel, lean) operating periods and oxidizing HC and CO by releasing stored oxygen during rich (relatively fuel-rich) operating periods. BACKGROUND ART Vehicle exhaust gas purification techniques for treating engine exhaust gases by promoting the gas are known.

Long-lived and long-lived TWC catalysts include one or more platinum group metals such as, for example, platinum, palladium, rhodium and ruthenium. These catalysts are supported on high surface area refractory oxide supports such as high surface area alumina. The support is supported on a suitable carrier or substrate, such as monolithic carriers such as refractory ceramic or metal honeycomb structures, or refractory particles such as spheres or short extruded pieces of suitable refractory material. Refractory oxide supports generally include alkaline earth metal oxides such as oxides of Ca, Sr and Ba, alkali metal oxides such as oxides of K, Na, Li, and Cs, and rare earth metal oxides such as oxides of Ce, La, Pr, and Nd. Oxygen storage components may be involved.

As high surface area refractory oxide supports, mention may be made of high surface area alumina materials, also referred to as 'gamma alumina' or 'activated alumina', and the BET (Brunauer, Emmett and Teller) surface area is typically 60 square meters per gram (m2 / g) As such, such activated alumina is typically a gamma and delta phase mixture of alumina but may contain significant amounts of eta, kappa and theta alumina phases. Precious metals such as platinum and / or palladium are supported or deposited on such a support.

U.S. Patent No. 4,294,726 discloses that a gamma alumina carrier material is impregnated with an aqueous solution of cerium, zirconium and iron salts, or the alumina is mixed with oxides of cerium, zirconium and iron, and then the material is calcined at 500 to 700 ° C in air, A platinum and rhodium containing TWC catalyst composition is disclosed which is obtained by impregnating the material with an aqueous solution of platinum and rhodium salts which have been dried and subsequently treated in a hydrogen containing gas at a temperature of 250 to 650 ° C. Japanese Patent Laid-Open Publication No. 19036/1985 discloses a catalyst for purifying exhaust gases having an increased ability to remove carbon monoxide at low temperatures. The catalyst comprises a cordierite substrate and two layers of activated alumina stacked on the surface of the substrate. The lower alumina layer contains platinum or vanadium deposited thereon and the upper alumina layer contains rhodium and platinum or rhodium and palladium deposited thereon. Japanese Patent J-63-205141-A contains platinum or platinum and rhodium in which the lowermost layer is dispersed on an alumina support containing rare earth oxides, and the top coating is dispersed on a support comprising alumina, zirconia and rare earth oxides. Laminated automotive catalysts comprising palladium and rhodium are disclosed. On the other hand, US Patent No. 4,587,231 discloses a method for producing a three-way catalyst for purification of exhaust gas.

Catalyst technology for internal combustion engine exhaust gas purification may be found in many other patents, but the prior art discloses supports having similar particle sizes.

Although catalysts of various compositions have been proposed, there is still a need for a catalyst having excellent low temperature activity and satisfying NOx performance in a high-speed driving section. That is, since most of the hydrocarbons (HC) are generated during the cold start process, excellent low temperature activity is required, and a catalyst capable of coping with the large amount of NOx generated in the high speed section of the automobile is desired.

The inventors have studied catalysts that can exhibit optimal performance from a new perspective. While the catalysts of the past have been focused on the change of composition, in this study, new concepts of catalysts were prepared and tested by varying the supports themselves, in particular the geometric distribution of the supports, and more specifically, the particle distributions. It was confirmed that the present invention was completed.

These embodiments consist of mixing with a first support of relatively large particles and a second support of relatively small particles, or with a spacer and a relatively small diameter of relatively large particles. The catalyst composed of a mixture of the second supports are excellent in low temperature activity and can achieve a deNOx improvement effect in a high-speed running section compared to the catalyst for purifying exhaust gas, thereby exemplifying that the economic and technical effects are superior to the conventional catalyst structure. While the invention has been described in detail with reference to specific embodiments, these embodiments are for illustration only, and the scope of the invention is defined by the appended claims.

1 is a schematic view of a catalyst composition composed of a single particle size support supported by a conventional noble metal coated on a substrate, and a catalyst composition composed of a bimodal support according to the present invention. (Bimodal particle size washcoat texture).
Figure 2 summarizes the conventional single support catalyst production method and bimodal particle distribution catalyst production method according to the present invention.
FIG. 3 is a photograph of a magnification 600 microscopy catalyst according to Example 1 and Comparative Example. FIG.
4 is a chart summarizing the THC, CO and NOx removal performance of Example 1 and Comparative Example catalysts.
FIG. 5 is a photograph of a catalyst 700 magnification electron micrograph according to a small particle support and a large particle support mixing ratio (13: 1-2.5: 1).
FIG. 6 is a test result showing that a catalyst having a high ratio of a second support to a first support at a 2: 5 level, that is, a catalyst having a high ratio of first support, which is a large particle, has improved performance over a low catalyst.
FIG. 7 is a photograph of a 600 magnification electron micrograph of a catalyst with small particle size variations.
8 is a test result showing that the larger the second support particles, the better the NOx performance.

In the catalyst composition for exhaust gas purification according to the present invention, the distribution of the support particles on which the precious metal component including platinum is supported is configured in a bimodal form. That is, a mixture composed of a first support of relatively large diameter particles and a second support of relatively small diameter particles, or a spacer of relatively large diameter particles, and a first of relatively small diameter particles. It can be mixed with two supports.

The first support or spacer may be a single or complex oxide in the range of 10-50 um and the second support may be a single or complex oxide in the range of 0.1-20 um. The single or composite oxide may be an activating compound selected from the group consisting of alumina, silica, zirconia, magnesia, ceria-zirconia, silica-alumina, alumino-silicate, alumina-zirconia, alumina-chromia and alumina-ceria, Preferably activated alumina. The first support or spacer may be composed of the same or different oxides as the second support. The weight mixing ratio of the first support or spacer and the second support may be 1.0 to 15.0. The precious metal deposited or loaded on the supports may be selected from the group consisting of Pd, Rh and Pt.

The catalyst composition for exhaust gas purification according to the present invention is alkaline earth metal oxides such as oxides of Ca, Sr and Ba, alkali metal oxides such as oxides of K, Na, Li and Cs, and rare earths such as oxides of Ce, La, Pr and Nd. Oxygen storage components (OSCs) can be included, including metal oxides (BMOs).

The catalyst composition for exhaust gas purification according to the present invention may be prepared on a monolithic carrier or substrate such as a refractory ceramic or metal honeycomb structure, or on a suitable carrier or substrate such as refractory particles such as spheres or short extruded pieces of a suitable refractory material. Can be supported.

When the catalyst composition is applied as a thin coating on a monolith carrier substrate, the proportion of components is typically expressed in grams (g / L) of material per unit volume (liters) of catalyst and substrate. This value includes the cell size of the gas flow passages in the various monolithic carrier substrates. As used herein, the term 'support' refers to an oxide structure that supports a noble metal component, and the term “spacing body” refers to an oxide structure that is mediated to ensure porosity between supports and does not include a noble metal component. The support or spacer herein may have various geometries, but preferably consists of spheres.

Although the present invention is described with reference to the following examples, the present invention is mainly described in terms of a support or spacer structure, and in the examples for measuring the exhaust purification effect, some of the precious metals except for Pt, for example, are easy to experiment. It is evident in other words that the Pt component can be included in the catalyst composition. Therefore, the description of the examples excluding the Pt component is for a simple comparative experiment, and it is apparent to those skilled in the art that this precious metal component Pt is not excluded from the claims of the present invention.

The bimodal support according to the present invention is promoted local heating is promoted low temperature activity, it is determined that the NOx improvement effect in the high-speed running section by improving the diffusion of reactants due to the increase in porosity due to the bimodal form.

1 is a schematic diagram of a catalyst coated with a substrate composed of a support supported by a conventional noble metal and a catalyst coated with a bimodal particle size washcoat formed from a bimodal support according to the present invention. texture). The bimodal supports according to the present invention consist of a first support (or spacer) and a second support, and FIG. 1 shows an example composed of a second support loaded with a spacer and a noble metal. The spacer is an oxide structure not loaded with precious metal. The first support or spacer may be a single or complex oxide in the range of 10-50 um, the second support may be a single or complex oxide in the range of 0.1-20 um, and the second support may contain platinum, palladium and / or rhodium components. Loaded.

2 shows a conventional catalyst production method having a single support and a bimodal particle distribution catalyst production method according to the present invention. As will be appreciated by those skilled in the art, conventional catalyst preparation methods exemplarily immerse alumina powder as a support in a palladium solution (palladium-nitrate), disperse by adding additional oxygen storage material (OSC) particles, and then The substrate is milled to a size of 15 μm (D90 = 15 μm). In contrast, in the catalyst according to the present invention, the alumina powder as the second support is immersed in a palladium solution (palladium-nitrate), an oxygen storage material (OSC) is added and dispersed, and then the particle size is <6 μm (D90 < 6 um) after wet milling, the first support having a relatively large particle size (D90 = 30 um) is further introduced into the wet mill vessel and dispersed, and coated on the substrate. Through this process, the first support may be loaded with a palladium component eluted from the wet milling solution on the surface of the first support, which is referred to as a 'first support'. However, after the wet milling, it is calcined at 550 degrees Celsius or more, and then dispersed in a medium free of palladium (for example, water and acetic acid), followed by further addition of a spacer having a relatively large particle size (D90 = 30um). No palladium component is deposited on the sieve surface, so it is referred to as the 'spacer' in distinction from the first support. Therefore, the catalyst according to the present invention is composed of a mixture of a first support or spacer having a large particle size and a second support loaded with a noble metal, and may further include thickening oxygen storage material (OSC) particles. .

Gamma-alumina powder impregnated with 4.00 g / l palladium-nitrate in 20.0 g / l Pd-loaded activated alumina After dispersing 90.0 g / L oxygen storage material (OSC), followed by wet milling process to store active alumina and oxygen The material was adjusted to a diameter of 6um or less. Subsequently, 30.0 g / l diameter 30um gamma-alumina powder was further dispersed in the milling solution to prepare a slurry having a bimodal support size. The slurry was coated onto a ceramic honeycomb structure with a number of cells per square inch (CPSI) of 600 and a wall thickness of 3.0 millimeters. Coating was performed by dipping the substrate (105.7 * 69) into the slurry and draining the slurry, then removing the excess slurry by compressed air injection. The coated honeycomb structure was dried at 120 ° C. for 4 hours and calcined at 550 ° C. for 2 hours to complete the catalyst. An electron micrograph of 600 magnification is shown in FIG. 3, and the porosity measured by Mercury Intrusion Porosimetry (MIP) was about 54%.

Comparative Example 1

Gamma-Alumina Powder Impregnated with 4.00 g / l Palladium Nitrate in 50.0 g / l Pd Loading Activated Alumina After dispersing 90.0 g / L of Oxygen Storage Material (OSC) and Wet Milling Process to Activate Active Alumina and Oxygen Storage The material was adjusted to a diameter of 15 μm and then treated in the same manner as in Example 1 to complete Comparative Catalyst 1. An electron micrograph at 600 magnification is shown in FIG. 3. The porosity measured by Mercury Intrusion Porosimetry (MIP) was about 35%.

[Test Methods]

The fresh catalysts were degraded in the engine bench deterioration mode corresponding to 80,000 km running of the vehicle, and then the catalyst performance was tested by the NEDC method. THC, CO and NOx removal performance is summarized in FIG. 4. That is, the catalyst performance according to the example in the NEDC mode was improved compared to Comparative Example 1.

Comparison of Catalyst Performance According to Mixing Ratio of First and Second Supports

A bimodal catalyst was prepared in the same manner as in Example 1, but the catalysts were prepared by adjusting the mixing ratio between relatively small particles and relatively large particles. Table 1 summarizes these particle mixing ratios, and electron micrographs at 700 magnifications for these catalysts are shown in FIG. 5.

Small Particle (g / L) Large Particle (g / L) Small Particle / Large Particle Ratio Sample A 130 10 13.0 Sample B 90 50 2.5

As a result of testing the catalyst performance according to the test method according to the test method according to Example 2, as shown in Figure 6, the ratio of the second support: the first support is a high particle ratio of the first support is 2.5, that is, a large particle catalyst Improved performance compared to lower catalysts.

Comparison of Catalyst Performance According to Secondary Support Particle Size

A bimodal catalyst was prepared in the same manner as in Example 1, but various catalysts were prepared by adjusting the size of relatively small particles. Table 2 summarizes the small particle sizes applied, and electron micrographs at 600 magnifications for these catalysts are shown in FIG. 7. As a result of testing the catalytic performance of the catalysts according to Example 3 according to the test method, as shown in FIG. 8, the larger the second support particles, the better the NOx performance.

Small Particle Size (micron) Large Particle Size (micron) Sample A 3 30 Sample B 6 30 Sample C 9 30

Claims (11)

Exhaust gas composed of a mixture of a first support and a second support, the particle diameter of the first support is larger than the particle diameter of the second support, the distribution of the support particles supporting the noble metal component in a bimodal form Purification catalyst composition. An exhaust gas composed of a spacer and a second support, the particle diameter of the spacer being larger than the particle diameter of the second support, and the distribution of the spacer and the precious metal component support support particles in a bimodal form. Purification catalyst composition. The exhaust gas of claim 1, wherein the first support is a single or complex oxide having a particle diameter in the range of 10-50 um, and the second support is a single or complex oxide having a particle diameter in the range of 0.1-20 um. Purification catalyst composition. 3. The exhaust gas purification method according to claim 2, wherein the spacer is a single or complex oxide having a particle diameter in the range of 10-50 um and the second support is a single or complex oxide having a particle diameter in the range of 0.1-20 um. Catalyst composition.  The method according to claim 3 or 4, wherein the single or composite oxide is alumina, silica, zirconia, magnesia, ceria-zirconia, silica-alumina, alumino-silicate, alumina-zirconia, alumina-chromia and alumina-ceria. Catalyst composition for exhaust gas purification, characterized in that the active compound selected from the group consisting of.  The catalyst composition for purification of exhaust gas according to claim 1, wherein the weight mixing ratio of the first support and the second support is 1.0 to 15.0.  The catalyst composition for purification of exhaust gas according to claim 2, wherein the weight mixing ratio between the spacer and the second support is 1.0 to 15.0.  The catalyst composition for exhaust gas purification according to claim 1, wherein the precious metal loaded on the first and second supports is selected from the group consisting of Pd, Rh and Pt.  The catalyst composition for purification of exhaust gas according to claim 2, wherein the precious metal loaded on the second supports is selected from the group consisting of Pd, Rh and Pt.  The catalyst composition for purification of exhaust gas according to claim 1 or 2, further comprising alkaline earth metal oxide, alkali metal oxide and rare earth metal oxide (BMO) and oxygen storage component (OSC).  An exhaust gas purification catalyst, wherein the catalyst composition for exhaust gas purification according to any one of claims 1 and 2 is supported on an exhaust gas purification carrier or a substrate.

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