KR20060108853A - A catalystic composition with ir for purification of exhaust gas - Google Patents

Abstract

The present invention relates to a catalyst composition for internal combustion engine exhaust gas purification, the catalyst composition for internal combustion engine exhaust gas purification comprising a support, a platinum component and an optional first platinum group metal component other than platinum, wherein the first platinum group metal component is 400 ppm It is related with the above iridium component, It is related with the catalyst composition for internal combustion engine exhaust gas purification containing the iridium component which can acquire the effect of improving low temperature activity and high temperature activity.

Iridium, three-way catalyst, low temperature activity

Description

Catalyst composition for internal combustion engine exhaust gas purification comprising iridium component {A catalystic composition with Ir for purification of exhaust gas}

1 is a graph of LOT measurement of fresh catalyst,

2 is a LOT measurement graph under aging conditions.

3 is a Sweep measurement graph of the fresh catalyst,

4 is a sweep measurement graph under aging conditions.

5 is a graph of HC, CO and NOx accumulation by FTP-75 mode,

6 is a summary diagram of the graph of FIG. 5.

The present invention relates to a catalyst composition for internal combustion engine exhaust gas purification, and more particularly to a catalyst composition for ignition comprising an iridium component in a catalyst of the type commonly referred to as a '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, HC and CO oxidation, which stores oxygen during lean (relatively low fuel) operation, is relatively advantageous for NOx reduction, and releases stored oxygen during rich (relatively fuel-rich) operation. It is known to treat the engine exhaust gas by promoting it.

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 used in conjunction with high surface area refractory oxide supports such as high surface area alumina coatings and the like. The support is supported on a suitable carrier or substrate, such as a monolithic carrier such as a refractory ceramic or metal honeycomb structure, or refractory particles such as spheres or short extruded pieces of suitable refractory material. Such supported catalysts generally include alkaline earth metal oxides such as oxides of Ca, Sr and Ba, alkali earth 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. Used with oxygen storage components, including

High surface area refractory metal oxides are often used as a support for various catalyst components. The surface area of Brunauer, Emmett and Teller (BET) of high surface area alumina materials, also referred to as 'gamma alumina' or 'activated alumina', for example, is typically greater than 60 square meters per gram (m ² / g), and such activated alumina is conventional As a gamma and delta phase mixture of alumina but may also contain significant amounts of eta, kappa and theta alumina phases. As a support for at least some of the catalyst components of a given catalyst, refractory metal oxides other than activated alumina can be used.

Meanwhile, the amount of oxygen in the engine exhaust gas is measured using an oxygen sensor, a so-called lambda (λ) sensor, and the oxygen-fuel mixture ratio in the engine injection system is determined so that the CO, HC, and NOx conversion ratios are optimal according to the measured oxygen partial pressure in the exhaust gas. do. The ideal mixing ratio is the mixing ratio (λ = 1), which is a condition under which only CO2, H2O and N2 can be released to the outside after conversion (oxidation and reduction) by a catalyst. The catalyst composition properties can be specified by light-off temperature (LOT), where LOT is defined as the temperature at which the conversion efficiency of the catalyst exceeds 50%.

U.S. Pat. No. 4,294,726 discloses that a gamma alumina carrier material is impregnated with an aqueous solution of cerium, zirconium and iron salts or mixed with alumina with oxides of cerium, zirconium and iron, respectively, and then fired at 500 to 700 ° C in air. Next, a platinum and rhodium containing TWC catalyst composition obtained by impregnating the material with an aqueous solution of platinum and rhodium salts, dried and subsequently treated in a hydrogen containing gas at a temperature of 250 to 650 ° C., is disclosed.

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 discloses that the bottom layer comprises platinum or platinum and rhodium dispersed on alumina support containing rare earth oxide, and the top coating is on a support comprising alumina, zirconia and rare earth oxide. Laminated automotive catalysts comprising dispersed 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 compositions for internal combustion engine exhaust gas purification can be found in many other patents, and the ideal composition of these catalyst compositions or composites will be designed to lower the LOT to increase the conversion rate during cold start of the engine and improve the overall conversion rate in addition to the cold start section. It is required to be designed to be. In the above-mentioned patented catalyst composition for exhaust gas purification, the rhodium component may be added to enhance the catalytic activity, while the rhodium solution may contain a very small amount of iridium in the preparation of the rhodium solution, but the small amount of the iridium component may be catalytically active. Since rhodium solution containing iridium below the permissible quantity was applied to the exhaust gas purification catalyst composition, only the rhodium solution exceeding the permissible quantity was not used as the treating solution. It is discarded or mixed with a third rhodium solution that contains very little iridium and is used in compliance with the acceptable amount.

The present invention relates to a catalyst composition, characterized in that iridium (Ir) is included in a catalyst composition for purification of exhaust gases, commonly referred to as a three-way conversion catalyst (TWC). TWC catalysts include HC and CO oxidation; And multifunctional in that NOx reduction can be catalyzed substantially simultaneously, and a catalyst composition in which a large amount of iridium is intentionally exhibited low temperature activity (LOT) and high temperature activity in comparison with conventional compositions in which iridium is present as an impurity in the rhodium component. Significantly improved, the effective oxidation and NOx reduction of HC and CO is possible.

In a preferred embodiment of the present invention, the catalyst composition consists of a support, a platinum component, an optional first platinum group metal component other than platinum, preferably rhodium containing palladium and an iridium component of at least an impurity. As is also known, it includes an optional oxygen storage component selected from the group consisting of alkaline earth metal components, alkali metal components and rare earth metal components.

An optional embodiment of the present invention provides a laminated catalyst composite, wherein the first layer of the laminated catalyst composite is selected from the group consisting of a first support, a first platinum component, and an alkaline earth metal component, an alkali metal component, and a rare earth metal component. Oxygen storage components. The first layer may further comprise a first zirconium component. The second layer of the laminated catalyst composite consists of a second support and a rhodium comprising a first platinum group metal component other than platinum, preferably palladium and an iridium component of at least an impurity. As is also known, the second layer may optionally further comprise a second zirconium component.

As described above, the catalyst composition having a rhodium component containing iridium more than the impurity disclosed in the present invention has improved remarkably in low temperature activity (LOT) and high temperature activity, thereby effectively oxidizing HC and CO, and effectively reducing NOx. have. The first and second supports may be the same or different compounds and may be selected from the group consisting of silica, alumina and titania compounds. Preferably, the first and second supports are activating compounds selected from the group consisting of alumina, silica, silica-alumina, alumino-silicate, alumina-zirconia, alumina-chromia and alumina-ceria. More preferably, the first and second supports are activated alumina. In addition, the first and second layer compositions may further comprise nickel, manganese or iron components useful for removing sulfides, for example hydrogen sulfide emissions, which are known.

When the catalyst composition is applied as a thin coating on a monolithic 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. Iridium ppm is the weight relative to rhodium in the rhodium solution. As used herein, the term 'catalyst metal component' or 'platinum metal component' or a description of a metal comprising the same refers to a catalytically effective form of the metal whether the metal is present in elemental form or as an alloy or compound, for example an oxide. it means. Furthermore, as mentioned, the term 'lean' treatment mode or operation means that the air stream to be treated contains more oxygen than the stoichiometric amount of oxygen necessary to oxidize its entire reducing substance content, eg HC. Example according to the present invention was carried out to measure the effect of iridium, except for platinum, which is essential for exhaust gas purification, except for Pt in the following example is for ease of experiments, the inclusion of Pt It is obvious from the word. Therefore, it is apparent to those skilled in the art that the description of the examples except for Pt is for a simple comparative experiment, and thus the inclusion of Pt is not excluded from the claims of the present invention.

<Example 1>

1 part of Rh containing 1200 ppm of iridium was introduced into 90 parts of gamma-alumina and 5 parts of Pd were added to 350 parts of gamma-alumina, each of which was introduced in the form of an aqueous solution diluted enough to fill all the pores. 30.2 parts of stabilized Ce-Zr compound (Ce-Zr complex containing 70% CeO 2) and 25.5 parts of Ba (OH) are added to the Pd-containing alumina to combine with a sufficient amount of DI-water and 2% acetic acid, and the known particle size distribution Milling until appears. 2.75 parts of Ba (OAc) 2 and ZrO (OAc) 2, respectively, were added to the Rh containing alumina and milled in the same manner as Pd-alumina. The milled slurries were shear mixed together and milled further for 10 minutes. The final Pd / Rh (Ir 1200 ppm) slurry was coated onto a ceramic honeycomb structure with 600 number of cells per square inch (CPSI) and a wall thickness of 4.0 millimeters. Coating was performed by dipping the substrate 105.7 * 115 into the slurry and draining the slurry, then removing excess slurry by compressed air injection. The coated honeycomb structure was dried at 110 ° C. for 4 hours and calcined at 450 ° C. for 2 hours.

<Example 2>

A catalyst was completed in the same manner as in Example 1 except that 1 part of Rh containing 784 ppm of iridium was used.

<Example 3>

A catalyst was completed in the same manner as in Example 1, except that 1 part of Rh containing 423 ppm of iridium was used.

Comparative Example

Except that 1 part of Rh containing iridium as an impurity (40 ppm) was used in the same manner as in Example 1, and this comparative example was applied to the current Rh solution.

<Test method>

LOT and Sweep were tested on fresh catalysts and aging catalysts treated under aging conditions: first, fresh catalyst was pretreated for λ = 0.98, 800 ° C. for 30 minutes, and then 240 LOT and Sweep were evaluated in the range of ℃ to 400 ℃. In addition, the fresh catalyst was aged in a furnace at 1000 ° C. for 50 hours, and then LOT and Sweep were evaluated after the same pretreatment. On the other hand, HC, CO, and NOx cumulative were tested for Example 1 and Comparative Example catalysts.

According to the fresh catalyst LOT test, the catalyst compositions according to Examples 1-3 and Comparative Examples were not significantly different as LOT = 280 ° C to 290 ° C, but in the case of an aged catalyst, the catalyst composition according to Examples 1-3 As LOT = 370 ℃ to 390 ℃, it can be seen that there is a significant LOT improvement in comparison with the case of LOT = 420 ℃ to 440 ℃ in the comparative example.

In addition, according to the fresh catalyst sweep test, it can be seen that the catalyst composition according to the comparative example had the worst NOx conversion rate, and the NOx conversion rate of Example 1-3 improved about 20% at the same lambda point. Significant improvement with increasing Ir. On the other hand, the accumulation test shows that the catalyst composition having 1200 ppm Ir has an improved conversion of HC (20%), CO (35%) and NOx (13%) as compared with that of impurities (40 ppm).

These examples exemplify that by adding iridium or more impurity, a low temperature activity and a high temperature activity improvement effect can be obtained, and thus the economic and technical effects are superior to the conventional catalyst composition. Although the invention has been described in detail with reference to specific embodiments, these embodiments are for illustration only, the scope of the invention being interpreted on the basis of the appended claims.

Claims (3)

In a catalyst composition for purification of exhaust gas of an internal combustion engine comprising a support, a platinum component and an optional first platinum group metal component other than platinum, the first platinum group metal component is rhodium containing 400 ppm or more of iridium components. Catalyst composition for engine exhaust gas purification. The internal combustion engine exhaust gas according to claim 1, wherein the support is an activating compound selected from the group consisting of alumina, silica, silica-alumina, alumino-silicate, alumina-zirconia, alumina-chromia and alumina-ceria. Purification catalyst composition. The catalyst composition for internal combustion engine exhaust gas purification according to claim 1, further comprising an optional oxygen storage component selected from the group consisting of an alkaline earth metal component, an alkali metal component and a rare earth metal component.

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