JP2005103409A - Exhaust gas cleaning device of internal combustion engine - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the technical problem that an alkali metal in a lean NOx catalyst has such properties as to move by heat from the inside of a catalyst layer to a cordierite substrate and causes a decrease in the quantity of the alkali metal in the catalyst layer to degrade the catalytic performance. <P>SOLUTION: In the exhaust gas cleaning device, the resistance to movement of an alkali metal is enhanced by decreasing the contact area between a catalyst layer and cordierite, decreasing the quantity and speed of alkali movement. Thus, erosion caused by the movement of an alkali to the substrate is prevented, and the cleaning capability is increased by increasing the quantity of an alkali metal carried by the substrate. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a catalyst for purifying carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx) contained in exhaust gas discharged from an internal combustion engine such as an automobile, and an exhaust gas purification apparatus using the catalyst. .

  Since lean burn engines, DI (Direct-Injection) engines operated by lean combustion, and diesel engines are operated at a theoretical air fuel ratio or higher, oxygen is excessively contained in the exhaust gas.

  In a gasoline engine for automobiles, a three-way catalyst generally used for exhaust gas purification can purify HC and CO contained in exhaust gas from lean burn engines, DI engines and diesel engines, but under lean combustion conditions, NOx cannot be purified.

  For this reason, development of a catalyst (lean NOx catalyst) that effectively purifies NOx in exhaust gas containing oxygen is advanced, and after NOx is once trapped in an adsorbent or the like, a catalyst that reduces and purifies the trapped NOx is put to practical use. Is progressing.

  The lean NOx catalyst not only increases the basicity of the NOx supplement used, but also increases the amount of use, in order to meet exhaust regulations that are becoming stricter year by year.

  Specifically, a large amount of alkali metals such as Na and K are supported, but the alkali metals generally have a property of easily reacting with cordierite used as a catalyst substrate at a high temperature.

  This reaction of alkali metal with cordierite is known as alkali attack. This alkali attack phenomenon reduces the amount of alkali metal in the catalyst layer, making it impossible to maintain sufficient purification performance.

  For this reason, for example, Patent Document 1 discloses providing an alkali affinity substance such as Si in the catalyst layer.

  Patent Document 2 discloses that an alkali migration suppression layer such as silica is provided on the cordierite surface.

JP 2000-279810 A JP 2002-095973 A

  However, in the catalyst of this patent document 1, although the movement of alkali metal to cordierite can be suppressed, since alkali reacts with Si in the catalyst layer, the catalyst does not have sufficient catalytic activity. There is a problem that the activity decreases.

  Similarly, in Patent Document 2, the migration of alkali metal to cordierite can be suppressed. However, when the reaction product with Si in the migration suppression layer does not have a sufficient catalytic activity, the alkali has a catalytic activity. There is a problem that it cannot be maintained.

  In view of the above-mentioned problems of the prior art, the present invention uses an exhaust purification catalyst that suppresses migration to cordierite by a physical method, and does not suppress alkali attack by utilizing a change in alkali chemical form, and the catalyst. The present invention provides an exhaust purification device and a purification method.

  In order to solve the above problems, the present invention has a carrier layer for supporting a catalytically active component and a substrate having a monolith structure for holding the carrier layer, and the contact area between the carrier layer and the substrate is increased. This is characterized by increasing the resistance of movement of the catalytically active component into the substrate and decreasing the amount or speed of movement of the catalytically active component into the substrate.

  In the present invention, the movement of the alkali metal component to the honeycomb substrate is suppressed, and the heat resistance performance of the catalyst can be effectively improved. In particular, in the lean NOx catalyst, it is possible to increase the amount of the catalytically active component that is an alkaline component in order to improve the purification performance.

  The present invention relates to a catalyst for purifying carbon monoxide (CO), hydrocarbon (HC), nitrogen oxide (NOx) contained in exhaust gas discharged from an internal combustion engine such as an automobile, and an exhaust gas purification apparatus using the catalyst, The present invention relates to an exhaust gas purification catalyst. In particular, the present invention relates to the suppression of the movement of the catalyst component for preventing the catalyst performance from being lowered due to the alkali component in the catalyst moving into the substrate by heat.

  The present invention relates to an exhaust gas purification apparatus or exhaust gas purification catalyst for an internal combustion engine using a catalyst, comprising a carrier layer for supporting a catalytically active component and a substrate having a monolith structure for holding the carrier layer. And reducing the contact area between the carrier layer and the substrate, thereby increasing the resistance to movement of the catalytically active component into the substrate and reducing the amount and speed of movement of the catalytically active component into the substrate.

  In the present invention, the contact area between the carrier layer and the substrate is reduced by providing a particle layer having an average particle size of 20 μm or more between the carrier layer and the substrate.

  Further, in the present invention, it has a catalyst comprising a carrier layer for supporting a catalytically active component and a substrate having a monolith structure that holds the carrier layer, and this carrier layer is a plurality of carrier layers, By reducing the contact area between the support layers, the resistance of the catalyst component in the support layer is increased, and the amount and speed of movement of the catalyst component into the substrate are reduced.

  In the present invention, by providing a particle layer having an average particle size of 20 μm or more between the carrier layers, the contact area between the carrier layers is reduced.

  Furthermore, the present invention is characterized in that the exhaust gas purifying catalyst is a catalyst capable of efficiently removing NOx in the exhaust gas even in an oxygen excess atmosphere, for example, a lean NOx catalyst.

  EXAMPLES Hereinafter, although this invention is demonstrated with a specific example, this invention is not restrict | limited by these Examples.

  An example of an embodiment of the present invention is shown in FIG.

"Example 1"
An alumina slurry composed of γ-alumina (average particle size 30 μm), nitric acid, an alumina precursor, and purified water was prepared as slurry 1.

  An alumina slurry composed of γ-alumina (average particle size 18 μm), nitric acid, an alumina precursor, and purified water was prepared as slurry 2.

  Slurry 1 was coated on a cordierite honeycomb so as to have a coating amount of 30 g / L and fired.

  This honeycomb was coated with slurry 2 so as to have a coating amount of 190 g / L and fired to prepare an alumina-coated honeycomb.

  The honeycomb produced in this manner was impregnated and fired with a NOx trapping component solution containing Na and K as main components, and further impregnated and fired with a dinitrodiammine Pt solution, a dinitrodiammine Pd solution, and a nitric acid Rh solution.

  The catalyst prepared by the above method was designated as “Example 1”.

  In Example 1, since a layer of alumina particles having a large particle diameter is formed between the substrate and the carrier layer, the alkali component as the catalytically active component is less likely to poison the substrate, and the alkali attack on the substrate is suppressed.

"Example 2"
Slurry 1 was coated on a cordierite honeycomb so as to have a coating amount of 15 g ¥ / L and fired.

  The honeycomb 2 was coated on the honeycomb so as to have a coating amount of 95 g / L and fired.

  The coating with the slurry 1 and 2 was performed once more, whereby an alumina-coated honeycomb having a coating amount of 190 g / L as in Example 1 was produced.

  The honeycomb thus prepared was impregnated with an impregnation liquid having the same components as in Example 1 and fired.

  The catalyst prepared by the above method was designated as “Example 2”.

  In Example 2, as in Example 1, a layer made of alumina particles having a large particle size is formed between the substrate and the carrier layer, so that the alkali component as the catalytically active component is less likely to poison the substrate, and the alkali attack on the substrate is performed. Is suppressed.

"Comparative example"
The slurry 2 was coated on the cordierite honeycomb so as to have a coating amount of 190 g / L and fired to prepare an alumina-coated honeycomb.

  The honeycomb thus prepared was impregnated with an impregnation liquid having the same components as in Example 1 and fired.

  The catalyst prepared by the above method was designated as “Comparative Example”.

"Experimental example"
The honeycomb catalyst was subjected to thermal durability of 830 ° C. × 60 hr in an air atmosphere furnace.

  The catalyst after durability was mounted on a commercially available 2.0 L lean burn vehicle.

  The lean burn vehicle was subjected to a 10-15 mode running test, and the amount of exhausted NOx was measured.

  The above evaluation method was designated as “Experimental Example”.

  The results of evaluating Examples 1 and 2 and a comparative example in an experimental example are shown in FIG.

  As is clear from FIG. 2, the catalyst of the present invention was superior in purification performance in the 10-15 mode to the comparative example. This is because a layer of alumina particles having a large particle size is formed between the substrate and the support layer, and the alkali component as the catalytically active component is less likely to poison the substrate, thereby suppressing alkali attack on the substrate.

Schematic of alkaline component movement suppression according to the present invention. The effect of the performance improvement by this invention.

Claims (12)

An exhaust gas purification device for an internal combustion engine using a catalyst,
A carrier layer for supporting the catalytically active component; and a substrate having a monolith structure for holding the carrier layer, reducing a contact area between the carrier layer and the substrate, and allowing the catalytically active component to enter the substrate. An exhaust gas purifying apparatus for an internal combustion engine, wherein the resistance to movement is increased and the amount or speed of movement of the catalytically active component into the substrate is reduced. In claim 1,
An exhaust gas purifying apparatus for an internal combustion engine, wherein a particle layer having an average particle size of 20 μm or more is provided between the carrier layer and the substrate, and a contact area between the carrier layer and the substrate is reduced. An exhaust gas purification device for an internal combustion engine using a catalyst,
A carrier layer for supporting a catalytically active component; and a substrate having a monolith structure for holding the carrier layer, wherein the carrier layer is plural, and the contact area between the carrier layers of the plurality of single layers is increased. An exhaust gas purifying apparatus for an internal combustion engine, characterized by increasing the resistance of movement of the catalytically active component in the carrier layer and decreasing the amount or speed of movement of the catalytically active component into the substrate. In claim 3,
An exhaust gas purifying apparatus for an internal combustion engine, wherein a particle layer having an average particle size of 20 μm or more is provided between the carrier layers to reduce a contact area between the carrier layers. In claim 1,
The catalytic active component of the catalyst of the exhaust gas purification apparatus is at least one element selected from alkali metals such as Li, Na, K, etc., and the element is supported on the carrier layer. Exhaust gas purification equipment for engines. In claim 1,
The exhaust gas purifying apparatus for an internal combustion engine, wherein the catalyst of the exhaust gas purifying apparatus is a catalyst for removing NOx in the exhaust gas in an oxygen-excess atmosphere.   A carrier layer for supporting the catalytically active component; and a substrate having a monolith structure for holding the carrier layer, reducing a contact area between the carrier layer and the substrate, and allowing the catalytically active component to enter the substrate. An exhaust gas purification catalyst for an internal combustion engine, characterized by increasing movement resistance and reducing the amount or speed of movement of the catalytically active component into the substrate. In claim 7,
An exhaust gas purifying catalyst for an internal combustion engine, wherein a particle layer having an average particle size of 20 μm or more is provided between the carrier layer and the substrate to reduce a contact area between the carrier layer and the substrate.   The support layer of the exhaust gas purification catalyst is a plurality of layers, and the contact area between the support layers of the plurality of single layers is reduced to increase the movement resistance of the catalytically active component in the support layer, and the catalyst activity An exhaust gas purifying apparatus for an internal combustion engine, wherein the amount or speed of movement of the component into the substrate is reduced. In claim 9,
An exhaust gas purification catalyst for an internal combustion engine, wherein a particle layer having an average particle diameter of 20 μm or more is provided between the carrier layers, and a contact area between the carrier layers is reduced. In claim 7,
The catalytic active component of the catalyst of the exhaust gas purification apparatus is at least one element selected from alkali metals such as Li, Na, K, etc., and the element is supported on the carrier layer. Exhaust gas purification catalyst for engines. In claim 7,
The exhaust gas purifying catalyst for an internal combustion engine, wherein the exhaust gas purifying device removes NOx in the exhaust gas in an oxygen-excess atmosphere.

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