JP2008223671A - Exhaust-emission purifying apparatus - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust-emission purifying apparatus in which NOx purifying rate can be enhanced, covering of catalyst resulting from adherence of hydrocarbons to carriers of porous body can be reduced, and life of catalyst activity can be increased. <P>SOLUTION: An exhaust-emission purifying apparatus includes a plasma processing device 21, provided on an exhaust pipe 8 for an internal combustion engine 1, for generating plasma by applying high voltage into the exhaust gas to activate noxious components contained in the exhaust gas and reactive components with the noxious components respectively; and a purification processing assembly 28 filled in the exhaust pipe 8 at downstream of the plasma processing device 21 for purifying the exhaust gas by subjecting the activated noxious-components and reactive components to react with each other. In the purification process assembly 28, silver (Ag) catalyst and vanadium pentoxide catalyst are carried in the porous carrier. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification device that purifies harmful components in exhaust gas exhausted from an internal combustion engine.

  Conventionally, a plasma processing apparatus is inserted into an exhaust passage as an exhaust gas processing apparatus for purifying nitrogen oxide (NOx) of exhaust gas in an oxygen-excess atmosphere during a lean burn operation of a gasoline engine vehicle. There is known an exhaust passage on the downstream side of which is filled with a purification treatment body supporting silver (Ag) on a porous carrier. (For example, patent document 1).

The plasma processing apparatus in this exhaust gas processing apparatus has a pair of discharge electrodes, and has a structure in which exhaust gas passes between the discharge electrodes. Is affected by the following discharge chemical reaction.
First, when oxygen molecules and water molecules in the exhaust gas are discharged, the following dissociation occurs.
O ₂ → 2O ^*
H ₂ O → H ^* + OH ^*
This O ^* and OH ^* react with hydrocarbons (HC) and nitric oxide (NO), which are harmful gases, and finally formaldehyde, acetaldehyde, nitrogen dioxide (NO ₂ ), one Carbon oxide (CO), carbon dioxide (CO ₂ ), and water (H ₂ O) are generated.
HC + O ^* (or OH ^* ) → formaldehyde, acetaldehyde, CO, CO ₂ , H ₂ O
NO + O ^* → NO ₂

Aldehydes and CO generated by this discharge chemical reaction are reducing gases, and NO ₂ is an oxidizing gas. When this highly reactive reducing gas and oxidizing gas are passed through the purification treatment body in the next stage, the reducing gas and the oxidizing gas react on the catalyst surface as shown in the following formula, and nitrogen (N ₂ ), Carbon dioxide (CO ₂ ) and water (H ₂ O).
Aldehydes (or CO) + NO ₂ → N ₂ , CO ₂ , H ₂ O (catalyst surface)
In this way, exhaust gas containing oxygen is subjected to discharge plasma treatment to convert harmful gases in the exhaust gas into highly reactive reducing and oxidizing gases, and further using a catalyst, To be cleaned.

However, the original hydrocarbon HC of aldehydes, which are NOx reducing agents, precipitates (coking) on the surface and pores of the porous carrier, and there is a problem that the catalytic performance is lowered by covering the active sites. It was.
For this, as shown in Patent Document 2, an appropriate amount of nickel having a higher oxidizing ability than silver is supported on the NOx selective reduction catalyst layer, thereby oxidizing the hydrocarbon and reducing the amount of hydrocarbon to an appropriate amount. Has proposed an exhaust gas treatment device that prevents coking of hydrocarbons and prevents a reduction in the NOx purification rate.

Further, as shown in Patent Document 3, by adding magnesium to the NOx selective reduction layer catalyst layer provided on γ-alumina that is a porous carrier, the amount of acid sites of γ-alumina is reduced. An exhaust gas treatment device that prevents coking of hydrocarbons and prevents a reduction in the NOx purification rate has also been proposed.
In other words, the acid point is a site of γ-alumina where a positive charge is localized and can attract an electron pair, and the addition of magnesium reduces the amount of acid site of γ-alumina, so that the hydrocarbon attracts the γ-alumina. Thus, the amount of adhesion is reduced, and the amount of coking in the surface and pores of γ-alumina is reduced.

Japanese Patent Laid-Open No. 2002-210366 (second page, second row to third row, FIG. 1) Japanese Patent Laying-Open No. 2004-283823 (second page, third line to eighth line, FIG. 3) JP 2004-306019 A (2nd page, 3rd line to 8th line, FIG. 3)

In the above Patent Document 2, by adding an appropriate amount of nickel and oxidizing (burning) hydrocarbon species, the amount of hydrocarbon species adhering to the surface and pores of the porous carrier is reduced, and hydrocarbon coking is performed. This prevents the NOx purification rate from decreasing.
However, hydrocarbons contained in the exhaust gas reaching the purification treatment body are mixed with various components in reactivity, and aldehydes that are effective for the NOx purification reaction generated in the upstream plasma processing apparatus. It contains such oxygenates.
Therefore, these aldehydes and highly reactive lower hydrocarbon species are preferentially oxidized (burned) by the oxidation catalyst with nickel added, and the remaining hydrocarbon species are less reactive aromatic hydrocarbons. However, it is not an effective reducing agent for NOx purification reaction, and only prevents the NOx purification rate from being lowered under excessive oxygen during lean burn operation.

  Moreover, in the said patent document 3, by adding magnesium and reducing the acid point degree of a porous carrier, the adsorption | suction power of a reducing species is reduced and the adhesion amount of the hydrocarbon to a porous carrier is prevented, and hydrocarbon However, since the NOx purification reaction on the catalyst surface is a reaction between the reducing agent adsorbed on the catalyst surface and NOx, the reduction in the amount of acid sites for adsorbing the reducing agent is As a result, the amount of reducing agent to be used for the reaction was reduced, and as in the case of Patent Document 2, the reduction in the NOx purification rate was only prevented.

  An object of the present invention is to solve the above-mentioned problems, and it is possible to improve the reaction rate with NOx and to purify the exhaust gas that can increase the life of the catalyst activity. The object is to obtain a device.

  An exhaust gas purifying apparatus according to the present invention is provided in an exhaust gas flow path of an internal combustion engine, generates a plasma by applying a high voltage in the exhaust gas, and reacts with harmful components and harmful components in the exhaust gas. A plasma processing apparatus that activates each component, and purification that is provided in the plasma processing apparatus or in the exhaust gas flow path downstream thereof, purifies exhaust gas by reacting the activated harmful component and the reactive component. In the exhaust gas treatment apparatus provided with a treatment body, the purification treatment body has a porous carrier carrying a silver (Ag) catalyst and an oxide catalyst having an oxygen addition ability.

  According to the exhaust gas purification apparatus according to the present invention, the reaction rate with NOx can be improved and the life of the catalyst activity can be extended.

  Hereinafter, an exhaust gas purifying apparatus according to an embodiment of the present invention will be described with reference to the drawings. In the drawings, the same or corresponding members and parts will be described with the same symbols.

Embodiment 1 FIG.
FIG. 1 is a sectional view showing a multi-cylinder internal combustion engine 1 in which an exhaust gas treatment apparatus according to Embodiment 1 of the present invention is incorporated. FIG. 1 shows only one cylinder of the multi-cylinder internal combustion engine 1.
In an internal combustion engine 1 for an automobile according to the present invention, a piston 3 that reciprocates in a cylinder 2 and forms a combustion chamber 4 in the cylinder 2 is provided. A crankshaft 6 is connected to the piston 3 via a connecting rod 5, and the piston 3 reciprocates as the crankshaft 6 rotates. An intake pipe 7 and an exhaust pipe 8 communicate with the combustion chamber 4. A throttle valve 9 that rotates and controls the amount of air taken into the combustion chamber 4 is provided inside the intake pipe 7. Yes.
The head of the cylinder 2 is provided with a fuel injection injector 10 whose tip is directed into the combustion chamber 4 and supplies fuel into the combustion chamber 4, and an ignition plug that ignites the air-fuel mixture in the combustion chamber 4. 11 is provided. The fuel injection injector 10 and the spark plug 11 are connected to an engine control controller 12, and the operation of the fuel injection injector 10 and the spark plug 11 is controlled by a signal from the engine control controller 12.

  In the internal combustion engine 1 configured as described above, the intake air sucked through the intake pipe 7 is excessively introduced into the combustion chamber 4 by the lean burn operation, and is mixed with the fuel supplied from the fuel injector 10. A mixture is formed. This air-fuel mixture is ignited by the spark plug 11 and burned. The burned air-fuel mixture is exhausted to the outside through the exhaust pipe 8 as exhaust gas.

  An exhaust gas processing apparatus 20 according to Embodiment 1 of the present invention includes a plasma processing apparatus 21 that is provided upstream of an exhaust pipe 8 and applies a high voltage to exhaust gas sent from the internal combustion engine 1, and this plasma processing. A purification treatment body 28 that purifies exhaust gas by reacting harmful components in the exhaust gas and reaction components that react with the harmful components activated by the device 21 is provided.

A high voltage power source 22 that supplies a high voltage to the plasma processing apparatus 21 is connected to the plasma processing apparatus 21. An intake air amount sensor 23 that measures the amount of intake air to be sucked in is provided in the intake pipe 7. An air-fuel ratio sensor 24 that detects an air-fuel ratio represented by a mass ratio of air and fuel in the exhaust gas is provided upstream of the plasma processing device 21 in the exhaust pipe 8. An exhaust gas temperature sensor 25 for measuring the exhaust gas temperature of the exhaust gas is provided downstream of the plasma processing device 21 in the exhaust pipe 8. A crank angle sensor 26 that detects the rotational speed of the crankshaft 6 is provided in the vicinity of the crankshaft 6.
The crank angle sensor 26, the intake air amount sensor 23, the exhaust gas temperature sensor 25, and the air / fuel ratio sensor 24 are connected to a plasma generation control device 27. The plasma generation control device 27 is composed of a computer having a CPU, a ROM, a RAM, and an interface circuit. The rotation speed of the crankshaft 6, the amount of intake air sucked into the intake pipe 7, and the exhaust gas temperature of the exhaust gas. The plasma processing conditions of the plasma processing apparatus 21 are adjusted by controlling the high-voltage power supply 22 based on the mass ratio of air and fuel in the exhaust gas.

The purification treatment body 28 is, for example, a honeycomb ceramic base material provided with γ-alumina, which is a porous carrier, and is an oxide catalyst having a silver (Ag) catalyst and an oxygen addition ability on the granular γ-alumina. Vanadium pentoxide (V ₂ O ₅ ) is supported.
Examples of harmful substances include nitrogen oxides (NOx), carbon monoxide (CO), and hydrocarbons (HC). The nitrogen oxides in the plasma are separated into nitrogen gas and oxygen gas to be purified, and plasma Carbon monoxide and hydrocarbons in it react with oxygen to be purified as carbon dioxide gas and water.

According to the purification treatment body 28 having the above configuration, NO and some hydrocarbon species in the exhaust gas discharged from the internal combustion engine 1 are oxidized to NO ₂ and oxidized to aldehydes in the plasma processing apparatus 21. Occurs.
Thereafter, the hydrocarbon species adsorbed on the acid sites of γ-alumina of the purification treatment body 28 cause an oxygen addition reaction by vanadium pentoxide having an oxygen addition ability arranged in the vicinity thereof, and aldehydes, organic acids and alcohols. Oxygenated compounds such as succinates are produced.
These oxygen-containing compounds work together with aldehydes generated in the upstream plasma processing apparatus 21 as effective reducing agents for NOx purification reaction, and a high NOx purification rate is obtained, and catalyst deterioration due to hydrocarbon coking is prevented. This can prevent and extend the service life.

In this embodiment, vanadium pentoxide is used as the oxide catalyst, but it is of course not limited to this, and if the electronegativity of the lattice oxygen of the metal oxide is a value within the following range, Good.
That is, the electronegativity of the lattice oxygen of the metal oxide is expressed by a Pauling scale expressed as a relative value with the electronegativity of fluorine (F) having the highest electronegativity among elements being 4.0, The higher the value, the higher the oxygen addition reaction to the organic matter, the lower the higher the dehydrogenation reaction. When the electronegativity χ of the metal oxide lattice oxygen is χ> 2.5, the oxidative addition reaction to the organic matter becomes dominant, so that it is more difficult to generate a dehydrogenated organic component that easily causes coking. Suitable for becoming.
Further, in the case of χ <3.5, the solid oxide can exist more stably and is suitable as a catalyst material. Therefore, it is desirable that 2.5 <χ <3.5.
In particular, vanadium pentoxide has a low reactivity among hydrocarbons and can oxidize aromatics that are difficult to be converted into oxygen-containing compounds by the plasma processing apparatus 21. Therefore, vanadium pentoxide is an oxide catalyst having an oxygen addition ability. Is suitable.

FIG. 2 shows the change over time in the purification rate of NOx discharged by steady operation of a lean burn engine when used with an Ag / γ-alumina catalyst in which a silver catalyst is supported on γ-alumina, which is a porous carrier, carrying silver catalyst and vanadium pentoxide .gamma.-alumina is a diagram comparing the case of using the _{(V 2 O 5 + Ag)} / γ- alumina catalyst.
From FIG. 2 obtained by experiments by the present inventor, the (V ₂ O ₅ + Ag) / γ-alumina catalyst has a higher NOx purification rate due to the effect of vanadium pentoxide, and the NOx purification rate over time. It was also found that the decrease in was low.

In the above embodiment, as shown in FIG. 3 (a), the purification treatment body 28 is provided with a granular γ-alumina, which is a porous carrier, on a honeycomb ceramic base material. Although the catalyst and the vanadium pentoxide catalyst are supported, as shown in FIG. 3B, the purification treatment body 28 is a first purification treatment section in which the vanadium pentoxide catalyst is supported on γ-alumina on the substrate. You may make it comprise 28a and the 2nd purification process part 28b which carry | supported the silver catalyst on the gamma-alumina on the base material provided downstream.
In this case, prior to the NOx purification reaction, the first purification treatment unit 28a converts to an oxygen-containing compound, and this oxygen-containing compound is supplied to the second purification treatment unit 28b. In the processing unit 28b, sufficient reducing gas is supplied, and NOx is purified at a high purification rate.
Further, as shown in FIG. 3 (c), the purification treatment body 28 includes a first purification treatment portion 28a carrying a vanadium pentoxide catalyst on a base material, and a γ on the base material separately provided downstream thereof. -You may make it comprise from the 2nd purification process part 28b which carry | supported the silver catalyst on the alumina.
In this case, since the first purification processing section 28a and the second purification processing section 28b can be manufactured separately, the manufacturing process of the purification processing body 28 is simplified.

In addition, as shown in FIG. 4, the plasma processing apparatus 21 may be filled with a purification processing body 28 that is a plurality of granular aggregates.
In this case, an AC high voltage or a pulsed high voltage is applied between the ground electrode in surface contact with the cylindrical outer tube of the plasma processing apparatus 21 and the high voltage electrode provided coaxially with the outer tube. As a result, plasma is generated in the space between the high voltage electrode and the outer tube, but the exhaust gas comes into contact with the purification treatment body 28 in this atmosphere, so that the exhaust gas is purified in a short time. .

In addition, the exhaust gas purifying apparatus of this embodiment is incorporated in a gasoline engine vehicle, and a case where harmful components of exhaust gas exhausted by combustion of an air-fuel mixture with an excessive amount of oxygen during lean burn operation has been described. However, the present invention is not limited to this, and can be applied to a diesel engine vehicle.
In addition to automobiles, the present invention can be applied to, for example, those that purify harmful components of exhaust gas exhausted from a ship engine.

It is sectional drawing which shows the internal combustion engine in which the exhaust-gas processing apparatus concerning Embodiment 1 of this invention was integrated. It is a figure which shows a time-dependent change of the NOx purification rate when using the exhaust-gas purification apparatus by Embodiment 1 of this invention. (A) is a schematic diagram of the purification process body of Embodiment 1 of this invention, (b), (c) is a schematic diagram which shows the modification of a purification process body. It is a schematic diagram which shows the modification of the exhaust gas processing apparatus concerning Embodiment 1 of this invention.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 1 Internal combustion engine, 2 Cylinder, 3 Piston, 4 Combustion chamber, 5 Connecting rod, 6 Crankshaft, 7 Intake pipe, 8 Exhaust pipe, 9 Throttle valve, 10 Fuel injection injector, 11 Spark plug, 12 Engine control controller, 20 Exhaust Gas processing device, 21 Plasma processing device, 22 High voltage power supply, 23 Intake air amount sensor, 24 Air-fuel ratio sensor, 25 Temperature sensor, 26 Crank angle sensor, 27 Plasma generation control device, 28 Purification processing body, 28a First purification Processing unit, 28b Second purification processing unit.

Claims (5)

A plasma processing apparatus provided in an exhaust gas flow path of an internal combustion engine, which generates plasma by applying a high voltage in the exhaust gas and activates a harmful component in the exhaust gas and a reactive component with the harmful component, respectively; ,
An exhaust gas processing apparatus provided with the plasma processing apparatus or a purification processing body that is provided in the exhaust gas flow path downstream of the plasma processing apparatus and purifies exhaust gas by reacting the activated harmful component and the reactive component. ,
The exhaust gas purifying apparatus according to claim 1, wherein the purification treatment body carries a silver (Ag) catalyst and an oxide catalyst having an oxygen addition ability on a porous carrier.   2. The exhaust gas purifying apparatus according to claim 1, wherein the oxide catalyst has an electronegativity of lattice oxygen of a metal oxide of 2.5 <χ <3.5.   The exhaust gas purification device according to claim 1 or 2, wherein the purification treatment body includes the oxide catalyst and the silver catalyst provided downstream thereof.   The said purification process body is comprised from the 1st purification process part which has the said oxide catalyst, and the 2nd purification process part which has the said silver catalyst separately provided downstream of this 1st purification process part. The exhaust gas purifying device according to claim 1 or 2, wherein The exhaust gas purification device according to any one of claims 1 to 4, wherein the oxide catalyst is vanadium pentoxide (V ₂ O ₅ ).

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