JPH03213612A - Exhaust gas purifying catalyst for diesel engine - Google Patents

Abstract

PURPOSE:To secure non-permeability and heat conductivity of a metal carrier so as to regenerate an absorption layer in a short time by applying the absorption layer made of zeolite or the like to the metal carrier, and carrying an active substance in the absorption layer. CONSTITUTION:In an exhaust gas purifying catalyst, a metal carrier 1 is coated with an absorption layer 2 carrying an active substance therein. In the metal carrier 1, a spiral wall 10 and a corrugated wall 11 define innumerable cells 12, thus forming a honeycomb structure. The absorption layer 2 is applied to the fixed portion of the walls 10, 11 for coating, and is made of at least one kind among zeolite, sepiolite, mordenite and montmorillonite. Platinum, palladium, rhodium and so on can be adopted for the active substance. Therefore, the metal carrier 1 is excellent in heat conductivity with non-permeability so that the absorption layer 2 can be regenerated in a short time.

Description

[Detailed Description of the Invention] [Industrial Application Field] The present invention relates to an exhaust gas purification catalyst for a diesel engine,
More specifically, the present invention relates to an exhaust gas purification catalyst that collects diesel particulates such as soot emitted from diesel engines and renders harmful components harmless.

[Prior Art] As a conventional exhaust gas purification catalyst for a diesel engine, a pellet catalyst is known which is composed of a pellet carrier and at least one of an active substance and an adsorbent supported on the pellet carrier. The pellet carrier is mainly made of T-alumina, and an active substance such as platinum or an adsorbent such as γ-alumina is supported on this pellet carrier to form a pellet catalyst.

Furthermore, a ceramic honeycomb catalyst is known that includes a ceramic honeycomb carrier and an adsorbent supported on the ceramic honeycomb carrier. The ceramic honeycomb carrier is mainly made of cordierite, and an adsorbent such as γ-alumina is supported on this ceramic honeycomb carrier to form a ceramic honeycomb catalyst.

These pellet catalysts and ceramic honeycomb catalysts are usually installed in stainless steel converters and are used in forklifts equipped with diesel engines and exhaust gas purification devices for automobiles. Exhaust gas is purified by adsorption with an agent or by rendering it harmless with an active substance such as platinum.

[Problems to be Solved by the Invention] However, since the above-mentioned conventional pellet catalysts and ceramic honeycomb catalysts are entirely made of permeable ceramic except for the active substance, they do not capture excessive amounts of unburned fuel and oil by capillary action. It was easy to collect. In addition, since the back pressure is high with pellet catalysts, the catalyst bed length is shortened.
It was difficult to purify exhaust gas at a low temperature of 80° C. during cold start and 100 to 150° C. during warm idle, and a large amount of particulates tended to adhere. For this reason, when conventional pellet catalysts and the like are used for a long period of time, their surfaces are poisoned by soot and their interiors are poisoned by unburned fuel and oil, deactivating their adsorption performance and activation performance. For this reason, after long-term use, these pellet catalysts are generally regenerated in forklift loading mode or full-speed climbing mode in order to burn soot and remove it as gas. For example, the forklift cargo handling mode performs lift relief or tilt relief at full speed and approximately 400
This is carried out under the condition of exhaust gas temperature of ~450°C.

However, the conventional pellet catalysts and the like have poor thermal conductivity because the entire carrier is made of ceramic, and even if regeneration treatment is performed, only the surface is regenerated. Therefore, if the device is used for a short period of time immediately after the regeneration process, there is a risk that the desorbed gas will be adsorbed to the regenerated surface due to the heat that is conducted from inside with a delay, and the entire device will be poisoned again.

In addition, after long-term use, the back pressure resistance is high due to soot poisoning the surface, and some flow paths are blocked, making it difficult for high-temperature exhaust gas to reach all areas even if regeneration treatment is performed. If the recovery of capacity is not sufficient and the regeneration process is continued for a long time, new problems will occur, such as impairing the durability of the cargo handling pump.

In addition, if these problems are to be solved by a ceramic honeycomb catalyst, it may be considered to make the wall portions forming the cells of the ceramic honeycomb carrier thinner. However, if this is done, the practical strength will be impaired to the extent that assembly is impossible.

The technical problem to be solved by the present invention is to provide a practical exhaust gas purification catalyst whose purification ability can be sufficiently recovered through a short-time regeneration process.

[Means for Solving the Problems] In order to solve the above problems, the exhaust gas purification catalyst of the present invention comprises a metal carrier and an adsorption layer coated on the metal carrier and made of at least one of zeolite, sepiolite, mordenite, and montmorillonite. and an active substance supported on the adsorption layer.

As the metal carrier, a metal honeycomb structure, foam metal, wire mesh, etc. can be used. The density of these can be selected in consideration of back pressure.

The adsorption layer made of at least one of zeolite, sepiolite, mordenite, and montmorillonite acts to adsorb particulates, HC, SOX, aldehydes, fatty acids, etc., and some of them act in the same way as active substances.

As active substances, platinum (Pt), palladium (Pd)
, rhodium (Rh), etc. can be adopted. Platinum and palladium have excellent HC and Co oxidation performance, and rhodium has excellent NOX reduction performance.

[Function] Since the metal carrier of the exhaust gas purification catalyst of the present invention has no permeability, it is difficult to collect excessive amounts of unburned fuel and oil, and even when used for a long period of time, the metal carrier does not have permeability. The carrier is not poisoned, only the adsorption layer is poisoned. If this exhaust gas purification catalyst is regenerated, the metal carrier, which has excellent thermal conductivity, will quickly transfer heat to the adsorption layer, making it easy to regenerate the entire adsorption layer. Because the piezoresistance is low, high-temperature exhaust gas easily spreads throughout the adsorption layer, regenerating the entire adsorption layer almost simultaneously and in a short time. Furthermore, since this exhaust gas purification device uses a metal carrier, it is strong enough to withstand practical use.

[Example] Hereinafter, an example embodying the present invention will be described with reference to the drawings.

As shown in FIG. 1, the exhaust gas purification catalyst of this example has the following features:
As shown in FIG. 2, the metal carrier 1 has a honeycomb structure in which countless cells 12 are formed by a spiral wall portion 10 and a corrugated wall portion 11, and the fixed portions of the wall portions 10 and 11 are coated. It consists of an adsorption layer 2 carrying an active substance. In the adsorption layer 2, there are countless pores (
(not shown) is formed. As shown in FIG. 3, this exhaust gas purification catalyst is installed in a jacket 3 and used as an exhaust gas purification device for a diesel engine. Such an exhaust gas purification catalyst could be obtained as follows.

First, a special heat-resistant and corrosion-resistant stainless steel metal carrier 1 (
Equivalent to 100 cells manufactured by BEHR, φ140×180L> was prepared.

Then, add sepiolite powder (manufactured by Ohmi Mining Co., Ltd., trade name Miraclay, average particle size 325 mesh > 2000) to 1 p of distilled water.
A slurry of about 300 CpS dispersed in the water was prepared. The metal carrier 1 was immersed in this slurry, and the excess slurry was blown away with air to uniformly coat the fixed portions of the wall portions 10 and 11 with the slurry. This was fired at about 600°C in the air. In this way, an adsorption layer 2 made of sepiolite of 20 CI/0 or more was coated.

Then, a platinum ammonium solution was prepared in which the water absorption amount and Pi concentration were adjusted so that the amount of Pt supported was 1 to 2 q/1. PT was supported on the adsorption layer 2 by impregnating the metal carrier 1 coated with the adsorption layer 2 in a platinum ammonium solution for a predetermined time and firing.

In this way, an exhaust gas purification catalyst of an example was obtained.

(Comparative example) Cordierite honeycomb carrier (manufactured by NGK Insulators 100
An exhaust gas purification catalyst using a cell with a diameter of 143.8 x 180 L was prepared.

(Evaluation) The exhaust gas purification catalysts of the examples and comparative examples were installed in a stainless steel converter 3 as shown in FIG. 3, and an exhaust gas purification device was assembled. Then, these exhaust gas purification devices were installed in a lift equipped with a 39 direct injection diesel engine, and the purification rate of formaldehyde was measured. Measurement is O'
Comparison of the number of cycles (times) of repeating full acceleration for 1 second and idle for 1 second under C atmosphere and the amount of formaldehyde discharged in a standard silencer muffler (%)
I sought a relationship with.

At this time, the exhaust gas purification catalyst of the example was difficult to collect excessive amounts of unburned fuel and oil, and the adsorption layer 2 was only poisoned by soot, etc., and the metal carrier 1 was and was not poisoned by oil. Furthermore, the exhaust gas purification catalyst of the example had an exhaust gas temperature of approximately 80° C. during cold start, and was able to adsorb harmful components such as particulates by moisture generated by dew condensation.

On the other hand, the exhaust gas purification catalyst of the comparative example easily collected unburned fuel and oil in excess, and the surface was poisoned by soot and the like, and the inside of the carrier was also poisoned by the unburned fuel and oil.

Therefore, as shown in FIG. 4, the exhaust gas purification catalyst of the example was more likely to adsorb formaldehyde even after long-term use than the exhaust gas purification catalyst of the comparative example.

After long-term use, regeneration treatment was carried out in forklift cargo handling mode, with lift relief at full speed and exhaust gas temperature at 1 m from the exhaust manifold outlet at approximately 450°C for 13 minutes.

As a result, the exhaust gas purification catalyst of the example has a metal carrier 1
As the heat was quickly transferred to the entire adsorption layer 2, the soot on the adsorption layer 2 was turned into dry carbon and peeled off by the exhaust gas.
It was easily removed by combustion.

In addition, the exhaust gas purification catalyst of the example has low back pressure resistance due to the cells 12 of the metal carrier 1, and the high temperature exhaust gas easily spreads over the entire adsorption layer 2, and has excellent warm-up characteristics for desorption. The released gas is supported on the adsorption layer 2.
It was effectively purified with water, etc., and there was no chance of poisoning again.

On the other hand, since the exhaust gas purification catalyst of the comparative example was made entirely of cosierite, the thermal conductivity was poor and the regeneration treatment was insufficient.

Therefore, as shown in Fig. 4, the entire exhaust gas purification catalyst of the example can be easily regenerated almost simultaneously, and the purification ability can be sufficiently restored to almost the same level as before use through a short regeneration process. Ta. On the other hand, the exhaust gas purification catalyst of the comparative example is
Even through reprocessing, it was not restored to its original state.

[Effects of the Invention] As detailed above, the exhaust gas purification catalyst of the present invention is a material in which a metal carrier is coated with an adsorption layer, so it is a practically excellent product that can sufficiently recover purification ability through regeneration treatment. It is.

[Brief explanation of drawings]

Figure 1 is a perspective view of the metal carrier used in the exhaust gas purification catalyst of the example, Figure 2 is an enlarged sectional view of the exhaust gas purification catalyst, and Figure 3 is a diesel engine equipped with the exhaust gas purification catalyst of the example. FIG. 4 is a cross-sectional view of the exhaust gas purification device shown in FIG. 4, and is a graph showing characteristics in the example and the comparative example. 1...Metal carrier 10.11...Wall part 12...
・Cell 2...Adsorption layer Fig. 1 1 U Fig. 3

Claims (1)

[Claims] (1) A diesel engine comprising a metal carrier, an adsorption layer coated on the metal carrier and made of at least one of zeolite, sepiolite, mordenite, and montmorillonite, and an active substance supported on the adsorption layer. Exhaust gas purification catalyst.