JPS58131123A - Filter for purifying exhaust gas in internal combustion engine - Google Patents

Abstract

PURPOSE:To reduce the generation amount of secondary sulfate, by using Ag in addition to one kind or more of a noble metal as a catalyst for purifying an exhaust gas. CONSTITUTION:As the catalyst of a filter for purifying an exhaust gas, one added with Ag in addition to one kind or more of a noble metal such as Pt, Pd, Rh, Ir, Au, Pb or Os. For example, a powdery mixture consisting of talc, Al(OH)3, alumina and clay is plsticized to be molded into a honeycomb like columnar body 2 and a material same to the aforesaid powdery mixture is supplied to the end part of the columnar body 2 to fill cells therewith every other cell so as to close only one side thereof at both ends to bake the resulting filled columnar body 2. This filled columnar body is immersed in a PdCl2 solution to adsorb Pd and, after baking, further immersed in a AgNo3 solution to adsorb Ag to obtain a filter for purifying an exhaust gas after baking.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a filter for treating exhaust gas from an internal combustion engine.

It is particularly desirable from an environmental standpoint to treat exhaust gases from automobile internal combustion engines so that they can be safely released into the atmosphere. However, in some types of engines, particularly diesel engines, the presence of particulates in the exhaust gas stream is a problem. These particles may be made of carbon, hydrocarbons, metals, etc., and may be generated by incomplete combustion of hydrocarbon fuels under special operating conditions. Conventionally, various techniques have been proposed to remove or minimize the fine particles. However, in the prior art, it has been found that although the aforementioned particulates are reasonably well removed by a properly constructed filter, if the particulates accumulate too much on the filter, it becomes saturated or becomes inoperable. The effect cannot be said to be completely satisfactory.

In addition, some types of filters have the disadvantage that sulfate, which is a secondary harmful component, increases significantly, which has an adverse effect on the human body.

SUMMARY OF THE INVENTION In view of the problems of the prior art as described above, an object of the present invention is to provide a filter for purifying exhaust gas of an internal combustion engine, which stably suppresses the emission of particulates over a long period of time and also releases less sulfate. It is something.

The present invention achieves the above object by providing a filter for purifying exhaust gas of an internal combustion engine, which uses silver in addition to at least one type of noble metal as a catalyst for purifying exhaust gas.

Conventionally, precious metals and other metals, their salts, oxides, etc. have been used as exhaust gas purifying catalysts, but the present invention is characterized by the use of silver in addition to these catalysts. In this way, when silver is used in combination, the combustion temperature of combustible components in fine particles is relatively lowered, although the cause is not necessarily clear, and the amount of fine particle emissions is therefore reduced, as well as the amount of secondary sulfate generated.

As used herein, "noble metals" refers to platinum, radium, rhodium, iridium, gold, rubidium, osmium, etc., and the terms "noble metals" and "silver" refer not only to those that exist as elemental metals, but also to those that exist as elemental metals. This term is used to include all forms of atoms and ions, such as salts and oxides. In addition, these noble metals and silver are supported on a conventional catalyst carrier to form a filter material, but the manner in which they are supported is not particularly limited in view of the essence of the invention.

The carrier may also be a foamed or honeycomb-shaped inorganic material (
A conventional carrier such as a carrier (cordierite, spinel, alumina, etc.), a foamed or linear metal, or a carrier with an inorganic layer formed on the surface of such metal can be used. A carrier having an activated alumina layer formed on the surface of cordierite is preferred.

The amount of noble metal and silver (herein means the amount of atoms or ions) in the filter 1 must be 502 or less in total and preferably 0.1 to 502 and 1 to 502, respectively, and silver 1 to 502, respectively. 201, 0.1 to 3 t of noble metal is optimal.

The present invention will be explained in more detail below using examples.

Example 1 A cordierite foam carrier (density 0.3 f/i, average pore diameter 0.5 wn, volume 0.4 t) was coated with activated alumina 50
0 parts by weight, alumina sol (pH 5, specific gravity 1.1, AI,
After immersing the slurry in a slurry consisting of 350 parts by weight of 0310% (the rest being water and an organic acid as a stabilizer) and 135 M parts of water, it was taken out, the excess slurry was blown off, and the mixture was heated to 120°C.
was dried for 3 hours, and then fired in an electric furnace at 800° C. for 1 hour to form an activated alumina coat layer. The coating amount is 20% by weight. Next, it is immersed in distilled water to absorb enough water, then immersed in 1 t of platinic acid 0.4 f/L aqueous solution to adsorb platinum to the activated alumina layer, taken out, blown off excess water, and dried. After that, it was baked at 500°C for 1 hour.

The amount of platinum supported is 12 to 1 of the carrier.

Next, this was further impregnated with 1 t of a 17 wt% silver nitrate solution, taken out, dried at 120°C for 3 hours, and then fired at 600°C for 2 hours.
(see figure).

Example 2 Si0251% by weight, Al, 0.35% by weight, MgO1
A powder mixture consisting of talc, aluminum hydroxide or alumina, and clay selected to have a chemical composition of 4 it% was plasticized to form a honeycomb-like cylinder (100 cells/in3, cell wall thickness 0.4 m, The bulk density is 0.4 f/cd, the volume is 1 t; see Figure 2 on the left in Figure 2), and then, as shown in the second Figure on the right, the ends of the cylinder are filled with a cylindrical material at every other cell and at both ends. Filled with the same material as above so that only one side of each was closed, dried and baked at 1400°C for 3 hours,
Next, it was immersed in distilled water to absorb enough water, then immersed in 1 t of an aqueous solution of 1 f/4 radium chloride to adsorb palladium, taken out, blown off excess water, and dried for 500 ml. It was baked at ℃ for 1 hour. The amount of palladium supported was 11 for the filter material 1. Next, add this to 17 silver nitrate
After immersing in 1 ton of wt% aqueous solution, take it out and heat it at 120"C.
After drying for 3 hours at 600°C for 2 hours, the amount of silver supported was 5
Filter material 2 (FIG. 2), which is % by weight, was obtained.

Comparative Example 1 Filter material 3 (
Figure 1) was obtained.

Comparative Example 2 Filter material 4 (FIG. 2) was obtained in the same manner as in Example 2, except that palladium was not supported on the ladle.

Tests and Results The filter materials 1 to 4 prepared in the above examples were placed in a metal container 10 as shown in FIG. 3, as shown in FIG. installed on the system, and the engine was set to 2000 rpm, 6KPf-
It was operated steadily at z, and the back pressure, particulate collection rate, and sulfate emission amount were measured for 20 hours. The results are summarized in the table below.

As is clear from the table, the filter material of the comparative example that supports only noble metals has a good result with a small increase in back pressure, but the particulate collection rate is low and the amount of sulfate discharged is abnormally large. On the other hand, in the example of the present invention in which silver was supported together with the noble metal, both the increase in back pressure and the amount of sulfate discharged were low, and the fine particle collection rate was high and favorable.

By using the filter for purifying exhaust gas of an internal combustion engine according to the present invention, flammable components of particulates contained in exhaust gas can be combusted at low temperature and with high efficiency.
/hr It is possible to burn the fine particles and render them harmless by using the thermal energy of the exhaust gas under normal operating conditions such as driving, and furthermore, the amount of sulfate generated secondarily can be reduced.

[Brief explanation of drawings]

Figure 1 is a perspective view of a filter material in which a catalyst is supported on a foamed ceramic, Figure 2 is a perspective view of a filter material in which a catalyst is supported in a cam-shaped ceramic, and Figure 3 is a perspective view of a filter material in which a catalyst is supported on a cam-shaped ceramic. FIG. 2 is a perspective view and a longitudinal cross-sectional view of a metal container for attachment to a system. 1.3... Foamed filter material, 2, 4... Nicum-like filter material, 10... Filter container, 11...
filter material.

Claims (1)

[Claims] 1. A filter for purifying exhaust gas from an internal combustion engine, characterized in that silver is used as a catalyst for purifying exhaust gas in addition to at least one kind of noble metal.