JP2900758B2 - High frequency heating element with catalytic function - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention uses high-frequency energy to heat and raise the temperature to catalytically decompose harmful substances such as hydrocarbons and carbon monoxide in exhaust gas discharged from internal combustion engines such as automobiles. The present invention relates to a high-frequency heating element.

[0002]

2. Description of the Related Art In automobiles that use gasoline as fuel, there is a movement to tighten regulations on the emission of hydrocarbons, carbon monoxide, and nitrogen oxides contained in exhaust gas. One of the purification methods of these pollutants is a post-treatment system using a catalyst. A typical catalyst is to control the air-fuel ratio to near the stoichiometric air-fuel ratio to oxidize hydrocarbons and carbon monoxide and reduce nitrogen oxides. At the same time, there is a catalytic body (three-way catalyst) that converts it into harmless carbon dioxide, water vapor, and nitrogen.

[0003] The catalyst body silica, alumina, 300-400 cells / inch ² of monolithic carrier of cordierite as a main component magnesia or iron, - chromium - metal support an aluminum-based alloy and corrugated (Metal On the carrier), or a coating layer called a wash coat made of fine particles of alumina or the like having a large surface area, or an oxide layer of the metal carrier, and platinum, palladium, rhodium, etc. The catalyst function is exerted by heating the exhaust gas.

Recently, an electric heater system has been studied in which an electric current is directly applied to the metal carrier to rapidly heat the catalyst body in order to exert a catalytic function in a short time.

[0005]

However, the above conventional configuration has the following problems.

That is, the conventional catalyst requires the catalyst layer to have a temperature of 350 ° C. or higher in order to exert the catalytic function. It took about one minute, and until then, there was a problem that harmful exhaust gas was directly discharged to the atmosphere.

[0007] Further, a heater-type catalyst body that rapidly heats by energizing the metal carrier improves the temperature rising speed as compared with a catalyst body that is heated only by the exhaust gas, but has a large heat capacity of the metal carrier, so that it takes an extremely short time. In addition to the problem that large power is required to raise the temperature, there is a problem that reliability such as electrical insulation is lacking.

The present invention solves the above-mentioned problem, and has a catalytic function of reducing harmful substances such as hydrocarbons and carbon monoxide in exhaust gas discharged when starting an engine of an automobile or the like by using high-frequency heating. It is intended to provide a high-frequency heating element.

[0009]

In order to achieve the above object, the high-frequency heating element having a catalytic function of the present invention is made of organic material.
It is obtained by coating and firing a porous material with a ceramic material.
A ceramic porous body which constitutes from said the high-frequency absorbing layer that absorbs the high frequency energy which is formed in the ceramic porous body fever, and the supported on a high-frequency absorbing layer catalyst.

The high-frequency heating element having a catalytic function of the present invention absorbs high-frequency energy in an organic porous body and generates heat.
It comprises a high-frequency absorbing porous body obtained by coating and firing a ceramic material, and a catalyst supported on the high-frequency absorbing porous body.

[0011]

In the above construction, when high-frequency energy is supplied to the high-frequency heating element having a catalytic function of the present invention, the high-frequency absorbing layer or the high-frequency absorbing porous body constituting the high-frequency heating element absorbs high-frequency energy and heat. Heated by conversion. At the same time, the catalyst supported on the high-frequency absorption layer or the high-frequency absorption porous body is heated, and when reaching a temperature that functions as a catalyst, carbon monoxide and hydrocarbons in exhaust gas discharged from automobiles and the like are decomposed by the catalyst, Converted to harmless carbon dioxide and water vapor and released into the atmosphere.

Since the high-frequency heating element has a skeleton made of a porous ceramic material, it is lighter in weight and can have a smaller heat capacity than a conventional catalyst. Therefore, the high-frequency heating element can be rapidly heated by high-frequency energy, and the heat energy can be efficiently transmitted to the catalyst, so that the temperature can be raised to a temperature that functions as a catalyst in a short time.

[0013]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a partial sectional view of a high-frequency heating element having a catalytic function according to an embodiment of the present invention. In the drawing, reference numeral 1 denotes a high-frequency heating element, and a high-frequency absorbing layer 3 made of a high-frequency absorbing material that absorbs high-frequency energy and generates heat is formed in a porous ceramic body 2, and a high-frequency absorbing layer 3 carries a catalyst 4. The ceramic porous body 2 has a three-dimensional net-like skeleton structure having uniform continuous pores 5 as shown in FIG.

The ceramic porous body 2 is obtained by coating an organic porous body such as polyurethane (for example, polyurethane foam) as a base material, coating a ceramic material on the base material, and firing the ceramic material. At least one of alumina, silica, magnesia, and zirconia having excellent mechanical strength is applied.

As a material for forming the high-frequency absorption layer 3, a semiconductor material having excellent high-frequency absorption characteristics can be mentioned, and in particular, oxides, carbides containing zinc, copper, manganese, cobalt, iron, tin, titanium and silicon as main components. A material composed of at least one complex oxide such as a perovskite complex oxide containing the metal is applied. The reason that the semiconductor material is excellent in high frequency energy absorption and heat generation characteristics is that the semiconductor material has conductive properties and dielectric properties suitable for high frequency absorption. In particular, by applying silicon carbide as a high-frequency absorbing material, more excellent high-frequency energy absorption / heating characteristics and heat resistance in an exhaust gas atmosphere,
Chemical stability can be achieved.

The catalyst 4 for decomposing harmful substances is platinum,
Palladium, noble metals of rhodium, copper, manganese, oxides of cobalt, perovskite-type composite oxides,
At least one of these applies.

The high-frequency absorbing material forming the high-frequency absorbing layer 3 and the porous ceramic body 2 is bonded with an inorganic binder, and the catalyst 4 is carried by bonding with the inorganic binder or by immersing and drying a catalyst solution. The inorganic binder is not particularly limited, but is preferably a colloidal particle of alumina, silica, zirconia or the like having excellent heat resistance and adhesiveness.

The high-frequency heating element 1 is manufactured as follows. A slurry comprising a high-frequency absorbing material, an inorganic binder, and a solvent (usually water) is prepared, and the ceramic porous body 2 is immersed in the slurry, or the slurry is applied to the ceramic porous body 2 by brushing or spraying. Then, after the high-frequency absorbing material and the inorganic binder are attached to form the high-frequency absorbing layer 3, drying or firing is performed. The composition of the slurry is appropriately set depending on the amount of the required high frequency absorbing material to be adhered, the amount of the inorganic binder capable of maintaining the adhesive strength, the operation during the immersion treatment, and the like. Next, a catalyst solution is prepared by dispersing (or dissolving) the metal catalyst 4 or the metal compound containing the catalyst 4, and the ceramic porous body 2 on which the high-frequency absorption layer 3 is formed is immersed in the catalyst solution. Alternatively, the catalyst solution is applied to the high frequency absorption layer 3 by spraying or the like, and then dried or fired. When the catalyst 4 is a metal oxide, the loading of the catalyst is performed as follows. A slurry comprising a catalyst 4, an inorganic binder, and a solvent is prepared, and the ceramic porous body 2 on which the high-frequency absorption layer 3 is formed is immersed in the slurry or applied by brushing or spraying, and then dried or fired. The catalyst 4 may be prepared by adding a predetermined amount to the slurry composed of the high-frequency absorbing material, the inorganic binder, and the solvent in advance, and carrying the high-frequency absorbing layer 3 simultaneously with the formation of the high-frequency absorbing layer 3.

Next, the function and effect of the high-frequency heating element having a catalytic function of the present invention will be described with reference to an exhaust gas purifying apparatus as an example.

FIG. 3 shows an example of an apparatus for purifying exhaust gas discharged from an automobile provided with the high-frequency heating element 1 having a catalytic function according to the present invention. In the figure, reference numeral 6 denotes an exhaust pipe for discharging exhaust gas of an internal combustion engine, 7 denotes a heating chamber provided in the middle of the exhaust pipe, and the high-frequency heating element 1 having a catalytic function of the present invention is housed in the heating chamber 7. You. Reference numeral 8 denotes a support member for supporting the high-frequency heating element 1 having a catalytic function accommodated in the heating chamber 7. The supporting member 8 includes an outer periphery of the high-frequency heating element 1 having the catalytic function and an inner wall of the heating chamber 7. It also has a thermal insulation function between the two. Reference numeral 9 denotes a high-frequency oscillator that generates high-frequency energy to be supplied to the heating chamber 7, and 10 denotes a waveguide that transmits high-frequency energy generated by the high-frequency oscillator 9 to the heating chamber 7. Numerals 11 and 12 denote high-frequency shielding means for limiting the heating chamber 7, and are composed of a metal plate having a large number of punched holes or a metal honeycomb structure having a large number of through holes.

When the engine of a gasoline vehicle starts, exhaust gas containing harmful substances such as carbon monoxide and hydrocarbons discharged from the engine flows through the exhaust pipe 6 and flows into the high-frequency heating element 1 having a catalytic function. On the other hand, when the high-frequency oscillator 9 generates high-frequency energy according to a command from a control unit (not shown) at the same time as or immediately before the start of the engine, the high-frequency energy is transmitted to the heating chamber 7 through the waveguide 10. Then, it is absorbed by the high-frequency absorber 1 (actually, the high-frequency absorption layer 3 formed on the ceramic porous body 2) and converted into heat. At the same time, the catalyst 4 carried on the high frequency absorption layer 3 is heated, and when the temperature reaches a temperature at which the catalyst functions as a catalyst, carbon monoxide and hydrocarbons, which are harmful substances in the exhaust gas, react with oxygen contained in the exhaust gas. Occurs and is decomposed into harmless steam and carbon dioxide. This harmless exhaust gas passes through the muffler and is exhausted to the atmosphere through the exhaust pipe 6.

(Example 1) As a ceramic porous body 2, a molded body (volume 10) made of alumina, silica, and magnesia was used.
0 cc, 15 cells / inch) and high frequency absorption layer 3
A high-frequency heating element 1 was manufactured using silicon carbide whiskers as a high-frequency absorbing material forming platinum and platinum as a catalyst 4 for decomposing harmful substances. Note that alumina sol was used as the inorganic binder. The manufactured high-frequency heating element 1 is shown in FIG.
Exhaust gas purification device (high frequency power consumption 1.5kW)
In the heating chamber 7, and the exhaust gas amount is about 300 l / min.
The engine (displacement: 2000 cc) was operated so that the exhaust gas temperature became 300 to 350 ° C., and the purification performance of hydrocarbons by a hydrocarbon analyzer was evaluated.
After 0 seconds, a purification rate of about 60% was obtained.

When noble metals such as rhodium and palladium and metal oxides of copper, manganese, iron and cobalt were used instead of platinum as the catalyst 4, a purification rate of 45 to 60% was obtained after 30 seconds of high frequency power supply. Was.

When no high-frequency energy was supplied in Example 1, the purification rate after 30 seconds was about 5%.

(Example 2) A molded body made of alumina and zirconia (volume: 100 cc,
15 cells / inch), zinc oxide whiskers as a high frequency absorbing material constituting the high frequency absorbing layer 3, platinum as a catalyst 4 for decomposing harmful substances, and a high frequency heating element 1.
Was prepared. Note that alumina sol was used as the inorganic binder. The high-frequency heating element 1 is housed in the heating chamber 7 of the exhaust gas purifying apparatus (high-frequency power consumption 1.5 kW) shown in FIG. 3, and the exhaust gas amount is about 300 l / min and the exhaust gas temperature is 30.
The engine (displacement 2000c)
The operation of c) was carried out to evaluate the purification performance of hydrocarbons by a hydrocarbon analyzer. As a result, a purification rate of about 55% was obtained 30 seconds after the high-frequency power supply.

As the high-frequency absorbing material constituting the high-frequency absorbing layer 3, oxides of copper, manganese, cobalt, titanium, tin, iron and silicon, mixtures thereof, and metals thereof are used instead of zinc oxide whiskers. When a composite oxide containing at least one species and a compound of titanium-silicon-carbon-oxygen was used, a purification rate of 40 to 55% was obtained after 30 seconds of high-frequency power supply.

As described above, the high-frequency heating element 1 having a catalytic function of the present invention can be applied to an exhaust gas purifying apparatus, and can achieve excellent purification performance by supplying high-frequency energy. By using a porous ceramic body as a support serving as a skeleton of the high-frequency heating element 1, the weight can be reduced as compared with a conventional catalyst body made of a cordierite carrier. As a result, the heat capacity of the high-frequency heating element 1 is reduced, and it can be considered that the purification performance is good because the temperature can be raised more quickly at the temperature functioning as a catalyst.

FIG. 4 is a partial sectional view of a high-frequency heating element having a catalytic function according to another embodiment of the present invention. The high-frequency heating element 12 includes a porous body 13 having a function of absorbing high-frequency energy and generating heat (hereinafter, referred to as a high-frequency absorbing porous body 13) and a catalyst 4 supported on the high-frequency absorbing porous body 13. The high-frequency absorbing porous body 13 has a structure similar to that of the ceramic porous body 2 described in FIG. 2, and is made of an organic porous body such as polyurethane (for example, polyurethane foam) as a base material, and absorbs high-frequency energy to generate heat. A three-dimensional network skeleton structure having uniform continuous pores obtained by coating and firing a ceramic material is applied.

The difference from the above-described high-frequency heating element 1 is that the high-frequency absorbing porous body constituting the skeleton of the high-frequency heating element itself absorbs high-frequency energy and generates heat, so that the high-frequency absorbing layer 3 is not required.

The high frequency absorption porous body 13 is made of the same material as the high frequency absorption layer 3 described above.

Example 3 A high-frequency absorbing porous body 13 made of silicon carbide (volume: 100 cc, 20 ce)
11 / inch) and platinum as a catalyst 4 for decomposing harmful substances, to produce a high-frequency heating element 12. Note that alumina sol was used as the inorganic binder. The high-frequency heating element 12 is housed in the heating chamber 6 of the exhaust gas purifying apparatus (high-frequency power consumption 1.5 kW) shown in FIG.
1 / min, the engine (displacement 2000 cc) was operated so that the exhaust gas temperature became 300 to 350 ° C., and the hydrocarbon purification performance was evaluated by a hydrocarbon analyzer. Purification rate was obtained.

As described above, the high-frequency heating element 13 can also obtain excellent purification performance. Since the heat capacity can be reduced by using the high-frequency absorbing porous body 14 that absorbs high-frequency energy and generates heat as the high-frequency heating element 13 as in the first and second embodiments, rapid heating becomes possible and the heat is catalyzed. 4 can be transmitted efficiently,
This is because the temperature can be raised more quickly to the temperature that functions as a catalyst.

The high-frequency heating element 8 having a catalytic function of the present invention can also be used as a means for decomposing oily smoke and odor discharged from a cooker such as an oven microwave oven.

[0035]

As described above, according to the high-frequency heating element having a catalytic function of the present invention, the following effects can be obtained.

(1) The skeleton of the high-frequency heating element is made of an organic porous material
Obtained by coating the body with ceramic material and firing
High frequency energy on ceramic or organic porous material
Coating and burning ceramic material that absorbs heat and generates heat
To use a high-frequency absorber obtained by
Since the weight can be reduced, the heat capacity can be reduced as compared with a conventional catalyst body comprising a cordierite carrier. Therefore, the temperature can be raised more quickly to the temperature that functions as a catalyst, and excellent exhaust gas purification performance can be obtained.

(2) Since the high-frequency heating element having a catalytic function of the present invention can be heated to a temperature at which it functions as a catalyst in a very short time, there is no need for the temperature of the catalyst section to rise due to the heat of the engine, and the catalyst is separated from the engine. Position. Therefore, it is possible to avoid a high-temperature environment in a situation where the exhaust gas temperature is high near the engine, such as when the vehicle is running at high speed, so that the deterioration of the high-frequency absorbing material and the catalyst material is significantly suppressed, and excellent durability can be realized. .

[Brief description of the drawings]

FIG. 1 is a partial sectional view showing a high-frequency heating element according to an embodiment of the present invention.

FIG. 2 is a diagram showing a skeleton structure of a porous ceramic body used for the high-frequency heating element.

FIG. 3 is a configuration diagram showing an exhaust gas purifying apparatus using the high-frequency heating element of the present invention.

FIG. 4 is a partial sectional view showing a high-frequency heating element according to another embodiment of the present invention.

Claims (7)

(57) [Claims] A ceramic material is coated on an organic porous material.
A porous ceramic body obtained by heating and firing, a high-frequency absorbing layer that absorbs high-frequency energy formed on the ceramic porous body and generates heat, and a catalyst that is supported by the high-frequency absorbing layer. High frequency heating element. 2. An organic porous material absorbing high-frequency energy.
It is obtained by coating and firing a heating ceramic material.
A high-frequency heating element having a catalytic function composed of a high-frequency absorbing porous body to be produced and a catalyst supported on the high-frequency absorbing porous body. 3. The high-frequency heating element having a catalytic function according to claim 1, wherein the main component of the ceramic porous body is at least one of silica, alumina and zirconia. 4. The high-frequency heating element having a catalytic function according to claim 1, wherein the high-frequency absorbing layer and the high-frequency absorbing porous body that absorb high-frequency energy and generate heat are mainly composed of a semiconductor material. 5. A high-frequency absorbing layer and a high-frequency absorbing porous body that absorb high-frequency energy and generate heat are oxides and carbides containing at least one of zinc, copper, manganese, cobalt, iron, titanium, silicon, and tin. The high-frequency heating element having a catalytic function according to claim 1 or 2. 6. The high-frequency heating element having a catalytic function according to claim 1, wherein the high-frequency absorbing layer and the high-frequency absorbing porous body that absorb high-frequency energy and generate heat are mainly composed of silicon carbide. 7. The high-frequency heating element having a catalytic function according to claim 1 or 2, wherein the catalyst comprises fine particles of platinum, rhodium and palladium and at least one of metal oxides of copper, manganese, cobalt and iron. .