JPH1077831A - Exhaust emission control device for engine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To combine the decrease of moisture in exhaust gas and the presence of a reducing agent such as CO, HC by providing a moisture decomposing means for decomposing moisture, released from a moisture eliminating means, to generate reducing hydrogen. SOLUTION: Until a moisture storage body 46b in a moisture eliminating means 42b in a branch passage 22b is saturated, a photocatalyst 50b is deactivated and does not act. When a moisture eliminating means 42a is energized, on the other hand, moisture stored in a moisture storage body 46a is released, brought into contact with the photocatalyst 50a and decomposed so as to generate reducing hydrogen H and OH. When the moisture absorbing capacity of the moisture storage body 45b is lowered, exhaust gas of an engine 10 flows to a branch passage 22a. At the same time, the moisture storage body 46a starts storing moisture in exhaust gas, and the photocatalyst 50a is deactivated. Exhaust gas passes the photocatalyst 50a without stopping and is fed to a catalytic converter 18. On the other hand, the release of moisture stored in the moisture storage body 46b is started. At the same time, the photocatalyst 50b is activated.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a device for purifying exhaust gas discharged from an engine, especially a vehicle engine.

[0002]

2. Description of the Related Art Nitrogen oxides (NO _x ), carbon monoxide (CO) and hydrocarbons (HC), which are harmful components in exhaust gas discharged from engines, particularly engines for vehicles such as automobiles.
Platinum (Pt), palladium (P) on a heat-resistant porous carrier such as cordierite
d), one or two noble metals such as rhodium (Rh), and nickel (Ni), cobalt (C
A three-way catalyst in which an oxide such as o) is supported as a catalyst component is widely used.

However, the three-way catalyst can efficiently purify harmful components in an operating region near the so-called stoichiometric air-fuel ratio where the oxygen concentration in the exhaust gas is approximately 1% or less. When the concentration is several% or more, that is, in the exhaust gas discharged from the lean combustion region of the Otto cycle engine and the diesel engine operated in an essentially oxygen-excess state, there is a disadvantage that the purification efficiency of harmful components is extremely low.

[0004] Therefore, the substance having a molecular sieve structure, such as various natural zeolite or synthetic zeolite, by supporting the transition metal, even at high concentration of oxygen in the exhaust gas the lean combustion region, to purify NO _x and HC For example, a catalyst which is generally known as a zeolite catalyst has been developed. A catalyst in which a transition metal is supported on a substance having a molecular sieve structure of this type (hereinafter, this type of catalyst is sometimes referred to as a molecular sieve structure catalyst) is produced by a reaction using CO or HC contained in exhaust gas as a reducing agent. effectively it is capable of removing NO _x.

[0005] However, it is known that the molecular sieve structure catalyst changes its crystal structure due to the presence of a small amount of water, and significantly reduces the NO _x removal performance in the exhaust gas. at least 5%, preferably without providing a means for reducing the 1% or less, be located within the exhaust gas passage molecular sieve structure catalyst alone can not be expected excellent nO _x reduction effect.

In order to solve the above-mentioned problems, a catalyst having a water gas reaction catalyst disposed in an exhaust gas passage on the upstream side of a catalyst having a molecular sieve structure, for example, a zeolite catalyst has been disclosed in Japanese Unexamined Patent Publication No. Hei.
-300631. However, in the proposed exhaust gas purifying apparatus, when water is removed by the water gas reaction catalyst, CO and H in the exhaust gas are removed.
Since C is used as the reducing agent, the downstream side of the molecular sieve structure catalyst, insufficient amount of reducing components in the exhaust gas necessary to exert NO _x removal function, not sufficient NO _x removal effect can be obtained inconvenience There is.

[0007]

DISCLOSURE OF THE INVENTION The present invention has been made in view of the above circumstances, and a catalyst having a molecular sieve structure can effectively reduce NO.
_x , which is a condition necessary for removing _x , that is, reduction of water in exhaust gas and the presence of a sufficient amount of a reducing agent such as CO and HC,
It is an object of the present invention to provide an exhaust gas purifying device for an engine that can achieve both.

[0008]

In order to achieve the above object, the present invention provides a catalyst in which a transition metal is supported on a substance having a molecular sieve structure and disposed in an exhaust passage of an engine, and an exhaust gas upstream of the catalyst. A water treatment device that is disposed in the passage and includes a water removal unit that stores moisture in exhaust gas and a water decomposition unit that decomposes water released from the water removal unit and generates reductive hydrogen. The present invention proposes an engine exhaust gas purifying apparatus characterized by the following.

In the present invention, there are provided two branch passages which are disposed in an exhaust passage upstream of the catalyst and to which exhaust gas is selectively supplied by a switching valve, and a water treatment device which is disposed in each of the branch passages. A control unit that operates the switching valve to supply the exhaust gas to the other branch passage when the moisture occlusion saturation of the moisture removing unit in the moisture treatment device in the one branch passage to which the exhaust gas is supplied is detected. The water removing means in the one branch passage, in which the supply of the exhaust gas is stopped by the switching valve, releases the occluded water, generates the reducing hydrogen by the water decomposing means, and supplies the exhaust gas. It is preferable that the water removing means in the other branch passage is configured to occlude water in the exhaust gas. It is preferably a photocatalyst that generates reducing hydrogen by decomposing more water.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be specifically described below with reference to the accompanying drawings. In the figure, reference numeral 10 denotes an engine conceptually shown, for example, an engine for a vehicle such as an automobile. The engine 10 is generated in an intake manifold 12 that takes in outside air via an air cleaner (not shown) and in the engine 10. An exhaust manifold for discharging the combustion gas to the outside air;
Together with the exhaust pipe connected to the discharge end of the engine 10
Is formed.

A catalytic converter indicated generally by reference numeral 18 is interposed downstream of the exhaust passage 16, and a catalyst 20 having a molecular sieve structure is accommodated inside the catalytic converter 18. Two branch passages 22 a and 22 b are provided between the exhaust passage 16 on the downstream side of the exhaust manifold 14 and the exhaust passage 16 on the upstream side of the catalytic converter 18. A switching valve 26 is provided at an upstream junction 24 of the branch passages 22a and 22b, and a valve shaft 2 of the switching valve 26 is provided.
A valve control lever 30 is fixed to 8.

An output end of an operating rod 34 driven by an actuator 32 is pivotally connected to the valve control lever 30. The actuator 32 may be an arbitrary actuator such as an electromagnetic actuator, an air cylinder device operated by compressed air, a pinion driven by an electric motor, and an electro-mechanical actuator including a rack bar meshing with the pinion. it can. Further, a moisture sensor 36 for detecting moisture contained in the exhaust gas is provided in the exhaust passage 16 between the downstream merging portion of the branch passages 22a and 22b and the catalytic converter 18. A signal or information indicating the detected water content Ew in the exhaust gas is supplied to a control unit 38 for controlling the actuator 32.

In the branch passages 22a and 22b, there are provided water treatment devices indicated generally by reference numerals 40a and 40b, respectively. The water treatment device 40a absorbs and stores moisture in exhaust gas. Means 42a and a water decomposing means 44a disposed downstream thereof. Similarly, the water treatment device 40b includes a water removing unit 42b that stores moisture in the exhaust gas and a water decomposing unit 44b that is disposed downstream thereof. The water removing means 42
a and 42b have substantially the same structure, and the water decomposing means 44a and 44b also have substantially the same structure.

The moisture removing means 42a and 42b can withstand high-temperature exhaust gas and have excellent corrosion resistance and chemical stability, such as alumina (Al ₂ O ₃ ) and silica (Si).
O ₂ ), zirconia (ZrO ₂ ), or other ceramic-based material, having porous micro-pores 46a, 46b having innumerable micropores, and water stored by heating the micro-pores 46a, 46b. And heating devices 48a and 48b for discharging the gas. The water decomposing means 44a and 44b are provided with photocatalysts 50a and 50b, respectively.
The photocatalysts 50a and 50b are provided with ultraviolet irradiation devices 52a and 52b for generating activity.

The catalyst 20 in which a transition metal is supported on a substance having a molecular sieve structure is generally called zeolite.
Main component is silica and alumina, Si / Al ratio is 5-1
It is about 00, and has a crystal structure of a metallosilicate such as X-type, Y-type, or ZSM-type, or a zeolite or metallosilicate obtained by ion-exchange with a transition metal.

The photocatalysts 50a and 50b are mainly composed of titania (TiO ₂ ) on a carrier made of alumina, cordierite or the like, and if necessary, iron oxide (Fe ₂ O).
₃ ) One or two or more additives such as copper oxide (Cu ₂ O) and nickel oxide (NiO) can be advantageously used. Further, the ultraviolet irradiation device 52
a and 52b are housed in a quartz glass container that withstands the high temperature of the exhaust gas and has enhanced impact resistance, and has a wavelength λ of 300 n.
It has a lamp that produces ultraviolet light of about m. Further, the specific shape and structure of the carriers of the photocatalysts 50a and 50b and the relative arrangement of the ultraviolet irradiation devices 52a and 52b are arbitrary.

FIG. 1 shows that the switching valve 26 controls the branch passage 22.
a is closed, the branch passage 22b is opened, and the exhaust gas of the engine 10 flows into the branch passage 22b. While the exhaust gas passes through the water occluding body 46b of the water removing means 42b provided in the branch passage 22b, the water content is effectively absorbed, and the water content becomes 5%.
% Or less, preferably 1% or less exhaust gas, and pass through the water decomposition means 44b which is at rest, and the catalytic converter 1
8 and contacts the molecular sieve structured catalyst 20 stored in the converter. The moisture in the exhaust gas is low and CO,
Since the reducing components such as HC are not lost on the way,
Even under excess atmosphere more oxygen than the stoichiometric air-fuel ratio condition exists, effectively NO _x are removed, at the same time CO, HC also be purified.

Until the water occluding body 46b in the water removing means 42b in the branch passage 22b is saturated, the water content Ew in the exhaust gas detected by the water sensor 36 is lower than the set value. As a result, the actuator 32 is deenergized, the switching valve 26 is held at the switching position indicated by the solid line in the drawing, and the heating device 48b of the moisture removing means 42b is also deenergized. Further, since the ultraviolet irradiation device 52b of the water decomposing means 44b is also deenergized, the photocatalyst 50b is deactivated and does not operate.

On the other hand, the heating unit 48a in the water removing means 42a in the branch passage 22a is energized by the control unit 38 and the water decomposing device 44a
Is irradiated, the water occluded in the water occlusion body 46a in the previous cycle is released by heating, comes into contact with the activated photocatalyst 50a, is decomposed, and the reducing hydrogen H and OH is formed. The reducing hydrogen H and OH are mixed with the exhaust gas having a low water content from the branch passage 22b and the catalytic converter 18
To enhance the reducing atmosphere required for NO _x purification of the molecular sieve-constituting catalyst 20, so that the NO _x purification efficiency is further improved.

As time elapses, the water absorbing body 46b in the branch passage 22b becomes saturated or nearly saturated and the water absorbing capacity decreases to a certain limit. Gradually increases,
The controller 38 energizes the actuator 32 based on a signal or information that the moisture sensor 36 has detected the moisture content Ew. By the urging of the actuator 32, the operating rod 34 is displaced upward in the figure, and the switching valve 26 is switched to the position shown by the dotted line via the valve control lever 30.
As a result, the exhaust gas of the engine 10 flows to the branch passage 22a, and the inflow to the branch passage 22b is cut off.

At the same time, the heating device 48a in the water removing means 42a of the branch passage 22a is deenergized, and the water occluding body 46a starts occluding water in the exhaust gas, and the ultraviolet irradiation device 52a of the water decomposing means 44a. Is deactivated, the photocatalyst 50a is deactivated, and the exhaust gas is
is supplied to the catalytic converter 18 without passing through a.

On the other hand, since the heating device 48b in the water removing means 42b of the blocked branch passage 22b is energized, the water occluded by the water occlusion body 46b starts to be released. At the same time, the ultraviolet irradiation device 52b of the water decomposing means 44b is energized, so that the photocatalyst 50b is activated, and the water released from the water occluding body 46b comes into contact with the photocatalyst 50b to be decomposed, thereby reducing hydrogen. H and OH are generated and supplied to the catalytic converter 18. Consequently, just as above, the purification of the NO _x in the exhaust gas is effectively carried out, also CO, purification of HC is performed.

In the above embodiment, the water treatment device 4
Moisture removing means 42a, 42b constituting 0a and 40b
And the water decomposing means 44a and 44b are shown as separate devices, respectively. However, the water removing means 42a and the water decomposing means 44a are housed in a common casing. The disassembling means 44b can also be accommodated.

[0024]

As described above, the exhaust gas purifying apparatus for an engine according to the present invention includes a catalyst in which a transition metal is supported on a substance having a molecular sieve structure and disposed in an exhaust passage of the engine;
Moisture disposed in an exhaust passage on the upstream side of the catalyst and comprising water removing means for storing moisture in exhaust gas and water decomposing means for decomposing water released from the water removing means to generate reductive hydrogen. characterized by comprising a processing unit, an oxygen excess state, moreover harmful components in the exhaust gas of the engine including a large amount of water, in particular usually an advantage capable of purifying difficult NO _x removal effectively .

Further, in the present invention, two branch passages disposed in the exhaust passage upstream of the catalyst and to which exhaust gas is selectively supplied by a switching valve, and a water treatment disposed in the branch passage, respectively. A control unit for operating the switching valve to supply the exhaust gas to the other branch passage when the water occlusion saturation of the moisture removing means in the moisture treatment device in the one branch passage to which the exhaust gas is supplied is detected. In the water removing means in the one branch passage in which the supply of exhaust gas is stopped by the switching valve, the occluded water is released and the reducing hydrogen is generated by the water decomposing means, and the exhaust gas is supplied. The moisture removal means in the other branch passage is configured to absorb moisture in the exhaust gas, so that the moisture removal means has a limited moisture storage capacity. Despite, during continuous operation of the engine, continuously to purify the constantly gas, and there is an advantage that can effectively perform. Note also, the water decomposition unit, by a photocatalyst to generate a reducing hydrogen by decomposing water by irradiation of ultraviolet light, effective to _the NO _x purification molecular sieve structure catalyzed by small energy consumption required to ultraviolet radiation There is an advantage that reductive hydrogen can be generated and purification efficiency can be improved.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a preferred embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 10 ... Engine, 14 ... Exhaust manifold, 16 ... Exhaust passage, 18 ... Catalytic converter, 20 ... Catalyst, 22a and 22b ... Branch passage, 26 ... Switching valve, 32 ... Actuator, 36 ... Moisture sensor, 38 ... Control unit,
40a and 40b ... water treatment device, 42a and 42b ...
Water removing means, 44a and 44b ... water decomposing means, 46
a and 46b: a water occluding body, 48a and 48b: a heating device, 50a and 50b: a photocatalyst, 52a and 52b: an ultraviolet irradiation device.

──────────────────────────────────────────────────の Continuation of the front page (51) Int.Cl. ⁶ Identification code Agency reference number FI Technical indication location B01J 29/04 ZAB F01N 3/28 ZAB 35/02 ZAB 301C F01N 3/28 ZAB B01D 53/36 ZABJ 301 102C

Claims (3)

[Claims] 1. A catalyst in which a transition metal is supported on a substance having a molecular sieve structure and which is disposed in an exhaust passage of an engine, and a water removal which is disposed in an exhaust passage upstream of the catalyst and occludes moisture in exhaust gas. An exhaust gas purifying apparatus for an engine, comprising: a water treatment device comprising: a water decomposing means for decomposing water released from the water removing means to generate reductive hydrogen. 2. A branch passage disposed in an exhaust passage upstream of the catalyst and selectively supplied with exhaust gas by a switching valve; a water treatment device disposed in each of the branch passages; And a control unit for operating the switching valve to supply exhaust gas to the other branch passage when the water occlusion saturation of the moisture removing means in the water treatment device in the one branch passage in which the water is supplied is detected. In the water removing means in the one branch passage in which the supply of the exhaust gas is stopped by the switching valve, the occluded water is released and the reducing hydrogen is generated by the water decomposing means, and the exhaust gas is supplied. 2. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the moisture removing means in the branch passage is configured to occlude moisture in the exhaust gas. 3. The exhaust gas purifying apparatus for an engine according to claim 1, wherein the water decomposing means is a photocatalyst that decomposes water by irradiation with ultraviolet rays to generate reductive hydrogen.