JPH0428884B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a filter used for treating exhaust gas from internal combustion engines of vehicles, particularly diesel engines. Exhaust gas from diesel engines contains fine particles made of carbon, hydrocarbons, metals, etc., and if these fine particles are emitted as they are, they cause air pollution. Therefore, various measures have been taken to prevent these fine particles from being released into the atmosphere, one of which is treatment with a filter. Although this filter treatment has a simpler structure than other methods, it can achieve the same effect as other methods in preventing the release of particulates from the system. Widely used. However, since filter processing is a mechanism that traps the particles within the filter, after a certain period of use, the filter becomes saturated with particles and becomes unable to trap any more, or becomes inoperable. It was closed. For this purpose, a catalyst is present in the filter,
Methods have also been proposed in which the captured particulates are burned, or a means for heating the filter is provided to burn the captured particulates. However, even with these methods, it is still not possible to sufficiently suppress the occurrence of the above-mentioned situation.
Furthermore, when this method of burning particulates is adopted, sulfate is generated,
This material was supposed to be released outside the system and cause air pollution. The present invention was made in view of these points,
Its purpose is to provide long-term stability and
An object of the present invention is to provide a high-performance exhaust gas filter for internal combustion engines. And to achieve this purpose,
The present invention provides an exhaust gas filter for an internal combustion engine, comprising:
A heat-resistant carrier having a porous inorganic material layer such as spinel or alumina supports iron oxide along with at least one noble metal selected from the group of platinum, palladium, and rhodium, and the amount of the iron oxide supported is It has a characteristic structure of 5 to 20g/. Each component of the present invention will be explained in detail below. The carrier has a shape such as a cylinder, and its structure is porous so that fine particles can be captured well. Specifically, foam structures that form open cells as shown in Figure 1 A and B, and structures that have a honeycomb-shaped radial cross-sectional shape as shown in Figure 2 A and B (hereinafter referred to as Honeycomb structure) is used. In the latter case, each hole extends linearly in the exhaust gas flow direction, so in a simple honeycomb structure, the fine particles do not collide with the carrier very much, so the trapping effect may not be sufficient. In such a case, one end of each hole should be closed, and when exhaust gas containing fine particles flows into the hole from the open end, it will inevitably collide with the closed end, causing each hole to be blocked. The liquid may flow to an adjacent hole through a porous partition wall defining the hole, and flow out from the adjacent hole (the discharge side end of this hole is an open end). Since the carrier with this shape and structure is heated up to the exhaust gas temperature (300°C to 1000°C), it is made of a material that can be stably used under these conditions, that is, a heat-resistant material, such as an inorganic material such as ceramic or metal. It is composed of In addition, when using a metal material, the above-mentioned structure (Fig. 1:
In order to obtain the structure shown in FIG. 2, it is preferable to form the linear objects into a three-dimensional network structure or a structure in which they are arranged in parallel, and to coat this with a porous inorganic substance. Precious metals include platinum (Pt) and palladium (Pd)
and rhodium (Rh). The amount supported is preferably in the range of 0.1 to 3 g per carrier. Further, as the iron oxide, for example, ferric nitrate made into an oxide by heating can be used, and the amount supported is preferably considerably larger than that of the noble metal. That is, the amount of iron oxide supported is required to be 5 to 20 g per filter 1, which is the final product. If the amount supported is within this range, a high particulate combustion rate of about 50% or more, and in some cases even more than 80%, can be obtained. In contrast, if the supported amount is less than 5g/
If the amount exceeds 20g/, a low particulate combustion rate of 40% or less can usually be obtained. Further, in order to support these noble metals and iron oxides on the carrier, it is preferable to form activated alumina (γ-alumina layer) on the carrier. In other words, the presence of the activated alumina layer allows noble metals to be adsorbed,
As a result, the carrier supports noble metals and the like. The amount of such activated alumina layer present is preferably 2 to 40% by weight based on the filter. Next, examples of filters made up of these components will be described in a table.

[Table] An example of manufacturing such a filter will be described below. Production Example 1 A commercially available foamed cordierite carrier was immersed in a slurry consisting of activated alumina, water, and alumina sol, then taken out, excess slurry was blown off, and the carrier was dried at 120°C for 3 hours. Thereafter, it was fired for 1 hour in an electric furnace at 800°C to form an activated alumina layer. Next, it is immersed in distilled water to absorb enough water, then immersed in a platinum chloride aqueous solution to adsorb platinum to the activated alumina layer, taken out, blown off excess moisture, dried, and heated at 500℃ for 1 hour. Bake for an hour.
Furthermore, after being immersed in a ferric nitrate aqueous solution, it was taken out, dried at 120°C for 3 hours, and then fired at 500°C for 1 hour to obtain a filter (No. 1). Production Example 2 Talc, aluminum hydroxide (or alumina) selected to be cordierite with a chemical composition consisting of silica, alumina and magnesia.
The mixture consisting of clay and clay was plasticized and formed into a honeycomb shape, each hole was closed as described above, and after drying, it was fired at 1400° C. for 3 hours.
Next, this carrier was immersed in an aqueous palladium chloride solution to adsorb palladium, taken out, blown off excess moisture, dried, and then calcined at 500° C. for 1 hour.
Furthermore, after being immersed in a ferric nitrate aqueous solution, it was taken out, dried at 120°C for 3 hours, and then fired at 500°C for 1 hour to obtain a filter (No. 2). Production Example 3 A honeycomb-structured carrier formed in the same manner as Production Example 2 was immersed in a slurry consisting of activated alumina, water, and alumina sol, then taken out, excess slurry was blown off, and the carrier was dried at 120°C for 3 hours. Thereafter, it was fired for 1 hour in an electric furnace at 800°C to form an activated alumina layer. The amount of alumina coating is 10% by weight. Next, it is immersed in distilled water to absorb enough water, then immersed in an aqueous rhodium chloride solution to adsorb rhodium to the activated alumina layer, taken out, blown off excess water, dried, and fired at 500℃ for 1 hour. do. Furthermore, after being immersed in a ferric nitrate aqueous solution,
It was taken out, dried at 120°C for 3 hours, and then fired at 500°C for 1 hour to obtain a filter (No. 3). Filters according to comparative examples (Controls 1 to 3) are manufactured in exactly the same manner except that no iron oxide is supported. The filter according to Comparative Example 1 (Control 1) was applied to Manufacturing Example 1, the filter according to Comparative Example 2 (Control 2) was applied to Manufacturing Example 2, and the filter according to Comparative Example 3 (Control 3) was applied to Manufacturing Example 3. Corresponds to each. On the other hand, as another control 4, a filter in which only iron oxide was supported without supporting any noble metal (the amount of iron oxide supported was 15 g/1) was also produced. Its production is similar to Production Example A below, but palladium chloride,
The procedure was followed except for the immersion step in the rhodium chloride mixed solution. Test Example 1 Using each of the filters thus obtained (Nos. 1 to 3, Controls 1 to 3), a filter device as shown in FIG. 3A and B was created as follows. A cushion material 2 made of thin metal wire is wound around the entire circumferential direction of the filter 1 (cylindrical body). These are attached to a ring-shaped holding member 3 on the inner peripheral edge of one end.
is press-fitted into the cylindrical member 4 fixed by welding through the ring-shaped cushion material 5 disposed in contact with the holding member 3. After that, the cylindrical member 4
A ring-shaped holding member 3' is press-fitted into the inner peripheral edge of the other end via a ring-shaped cushion material 5'. Thereafter, the conical members 6, 6' were welded to both ends of the cylindrical member 4 to obtain a filter device 7. Note that each member is made of a heat-resistant material. Then, this filter device was attached to a diesel engine with a displacement of 2.2, and the engine was operated steadily (2000rpm; 6kgm), and the back pressure increased after 20 hours.
The particulate collection rate (to be understood as the percentage of particulates not released outside the system) and the amount of sulfate emissions were measured. The results are shown in Table 2 below.

【table】

[Table] As can be understood from the above table, the filters (No. 1, 2, and 3) according to the examples all have a back pressure increase of 3 mm.
Good results have been achieved with a fine particle collection rate of over 70% and sulfate emissions of less than 0.3g/hour. There is no comparison at all with filters according to comparative examples (Controls 1 to 3) in which no iron oxide is supported.
On the other hand, Control 4 has a poor particle collection rate and a very large increase in back pressure, making it unsuitable for practical use. This is fully achieved using the thermal energy from the exhaust gas under normal operating conditions (40 km/h). Production Example A A commercially available cordierite foam carrier (used in Table 1) was immersed in a slurry consisting of activated alumina, water, and alumina sol, then taken out, the excess slurry was blown off, and the support was heated at 120°C for 3 hours. Dry. Thereafter, it was fired for 1 hour in an electric furnace at 800°C to form an activated alumina layer. Next, it is immersed in distilled water to absorb enough water, and then immersed in a mixed solution of palladium chloride and rhodium chloride to adsorb palladium and rhodium onto the activated alumina layer, and then taken out to remove excess water. After blowing off and drying, bake at 500℃ for 1 hour. Further, this was immersed in an aqueous ferric nitrate solution, taken out, dried at 120°C for 3 hours, and then fired at 500°C for 1 hour to obtain Filter A. Production Example B Filter B was obtained according to the same procedure as Production Example A, except that a cobalt nitrate aqueous solution was used instead of the ferric nitrate aqueous solution. Production Example C Filter C was obtained according to the same procedure as Production Example A, except that a nickel nitrate aqueous solution was used instead of the ferric nitrate aqueous solution. Test Example 2 For each of the filters produced in Production Examples A to C, the combustion rate of particulate at 300° C. after entering the gas was measured according to a conventional method. The incoming gas is a N ₂ -O ₂ based gas, and the ratio of N ₂ and O ₂ in the gas is 90:10. Test Example 3 Regarding the filter produced according to Production Example A,
While varying the amount of iron oxide supported, the particulate combustion rate was measured for each amount of supported iron oxide. The measurement conditions are the same as in Test Example 2. The measurement results for Test Example 2 are shown in Table 3 below, and the results for Test Example 3 are shown in FIG.

[Table] From Table 3, the combination of noble metal (Pd-Rh) and iron oxide is much more efficient in collection than the combination of noble metal (Pd-Rh) and cobalt oxide or nickel oxide. It can be seen that fine particles can be combusted by exhaust gas energy. Also, from Figure 4, the amount of supported iron oxide is 5~
It can be concluded that exhaust gas treatment can be carried out most effectively within the range of 20g/. According to the present invention, the following effects are achieved. Particulates that are harmful components of air pollution can be efficiently captured, and the captured particulates can be sufficiently combusted using only the energy of the exhaust gas, so a stable exhaust gas treatment state can be maintained.
In addition, sulfate, which is a secondary harmful component, is hardly generated.

[Brief explanation of drawings]

Figures 1A and 1B are an external view A and a partial cross-sectional view A, and Figure 2A,
A is an external view A and a partial sectional view B showing another structure of the filter, FIGS. It is a graph showing the change in particulate combustion rate with respect to the amount of iron oxide carried in the filter of the invention. 1...Filter.

Claims (1)

[Claims] 1 A heat-resistant carrier having a porous inorganic material layer such as spinel or alumina supports iron oxide along with at least one noble metal selected from the group of platinum, palladium, and rhodium, and the amount of the iron oxide supported An exhaust gas filter for an internal combustion engine, characterized in that the amount is 5 to 20 g/.