Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Mixture is exhaust from internal-combustion engine
Reexamination Certificate
1998-08-14
2001-09-11
Dunn, Tom (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Mixture is exhaust from internal-combustion engine
C423S239100, C502S302000, C502S345000, C502S346000, C502S355000
Reexamination Certificate
active
06287527
ABSTRACT:
TECHNICAL FIELD
The present invention relates to catalysts and a method for controlling (purifying) the emission of exhaust from an internal combustion engine. The present invention relates more particularly to catalysts and a method for controlling the emission of exhaust, capable of reducing injurious (noxious) components, particularly NO
x
(nitrogen oxide), contained in the exhaust by decomposition and of removing particulate matter, unburned hydrocarbon, and carbon monoxide by combustion.
BACKGROUND ART
NO
x
in the atmosphere is the cause of photochemical smog and acid rain. Hence, the discharge of NO
x
from moving sources like automobiles incorporating internal combustion engines, such as gasoline engine and diesel engine, poses a social problem. The internal combustion engine is one of the NO
x
sources. Therefore, there is a tendency towards tightening up the laws and regulations concerning the amount of discharge of NO
x
. Accordingly, the development of exhaust emission control catalysts is being actively carried out.
As a conventional exhaust emission control catalyst for controlling the emission of exhaust from the gasoline engine, a so-called three-way catalyst capable of simultaneously reducing NO
x
, unburned hydrocarbon, and carbon monoxide is known. Since the exhaust from a typical gasoline engine contains very little oxygen, it is possible to achieve efficient reduction of NO
x
by unburned hydrocarbon or carbon monoxide, and decrease NO
x
.
However, the exhaust from the diesel engine contains excessive oxygen because of its engine characteristics. Moreover, stoichiometrically, the exhaust from the diesel engine contains less hydrocarbon and carbon monoxide which function as a reducing agent compared to NO
x
. Therefore, when a conventional three-way catalyst is used for the treatment of the exhaust from the diesel engine, NO
x
can hardly be decreased.
Furthermore, since the exhaust from the diesel engine contains a large amount of particulate matter formed by carbons, soluble organic fractions (SOF), sulfate, etc., the amounts of these elements discharged are restricted by the laws and regulations. Therefore, when using a typical three-way catalyst for the treatment of the exhaust from the diesel engine, it is also required to reduce the particulate matter. However, such a catalyst can hardly decrease the particulate matter.
In resent years, a lean burn gasoline engine, and a cylinder injection of fuel type gasoline engine have been developed for the purpose of decreasing the fuel consumption. Since these engines cause lean burn, the oxygen concentration in the exhaust from these engines is high. Therefore, when a typical three-way catalyst is used for the treatment of the exhaust from such gasoline engines, it is difficult to decrease NO
x
.
In order to solve this problem, a catalyst containing a porous carrier like zeolite carrying copper is proposed as an exhaust emission control catalyst which effectively removes NO
x
in exhaust containing a large amount of oxygen, such as exhaust from the diesel engine and exhaust from the lean burn gasoline engine. An example of such a catalyst is disclosed in Japanese Publication for Unexamined Patent Application No. 100919/1988 (Tokukaisho 63-100919). However, this catalyst is inferior in heat resistance, and its NO
x
removing ability tends to be lowered by sulfur oxides like SO
2
contained in the exhaust. Namely, there is a problem that the catalyst is readily poisoned.
Moreover, Japanese Publication for Unexamined Patent Application No. 137963/1993 (Tokukaihei 5-137963) discloses an exhaust emission control catalyst containing platinum as a principal component. However, since this catalyst is highly active to oxidize SO
2
in the exhaust, a large amount of sulfates are produced by the oxidation of SO
2
, resulting in an increase in the content of sulfates in the exhaust. Thus, there is a problem that this catalyst increases the amount of particulate matter in the exhaust due to the sulfates. In particular, in the case of the exhaust from a diesel engine which contains a larger amount of particulate matter compared to a gasoline engine, it is required to reduce the discharge of the particulate matter to a lower level. Hence, there is a more serious problem with respect to the exhaust from the diesel engine, namely an increased amount of particulate matter is produced.
Furthermore, Japanese Publication for Unexamined Patent Application No. 219147/1992 (Tokukaihei 4-219147) discloses an exhaust emission control catalyst containing a particular zeolite which carries cobalt, copper and/or rhodium, and rare earth metal as essential components.
However, only an exhaust emission control catalyst using lanthanum or cerium as the rare earth metal is disclosed as an example in this publication. When lanthanum or cerium is used as the rare earth metal, the activity of oxidizing SO
2
in the exhaust becomes higher. Therefore, when this catalyst is used for the treatment of high temperature exhaust from a diesel engine, a large amount of sulfates are produced by the oxidation of SO
2
, resulting in an increase in the content of the sulfates in the exhaust. Thus, like the above-mentioned catalyst, this catalyst causes a problem that the amount of particulate matter in the exhaust is increased.
Considering the above-mentioned conventional problems, it is an object of the present invention to provide exhaust emission control catalysts and a method for controlling the emission of exhaust, which can efficiently decrease NO
x
in exhaust containing a large amount of oxygen like exhaust from a diesel engine, and reduce the amount of particulate matter in the exhaust under high temperature conditions.
DISCLOSURE OF THE INVENTION
In order to achieve the above-mentioned object, the present inventors eagerly studied exhaust emission control catalysts, and found that an exhaust emission control catalyst having a catalytic component containing copper, praseodymium, and yttrium has an excellent ability that is not seen in the conventional exhaust emission control catalysts. The inventors completed the present invention based on the results of the study.
Namely, in order to solve the above-mentioned problems, exhaust emission control catalysts of the present invention are characterized in having the catalytic component containing copper, praseodymium, and yttrium.
Moreover, in the exhaust emission control catalysts of the present invention, at least one kind of element selected from the group consisting of cobalt, iron, nickel, lanthanum, cerium, and neodymium is preferably added to the catalytic component.
Furthermore, a preferred weight ratio of copper, praseodymium, and yttrium in terms of their oxides is that praseodymium oxide is 0.2 to 20 weight parts and yttrium oxide is 0.2 to 20 weight parts based on 1 weight part of copper oxide.
Additionally, in the exhaust emission control catalysts of the present invention, it is preferred that the catalytic component is carried in inorganic oxide which is formed from at least one of zirconia and zeolite.
In this structure, the exhaust emission control catalyst can efficiently reduce and decompose NO
x
in the exhaust containing a large amount of oxygen. Moreover, the exhaust emission control catalyst not only burns injurious components contained in the exhaust, such as unburned hydrocarbon and carbon monoxide, but also burns SOF as particulate matter. Furthermore, since the exhaust emission control catalyst can suppress the oxidative reaction of SO
2
in the exhaust, it is possible to reduce the amount of particulate matter produced from sulfate by the oxidation of SO
2
.
Consequently, such an exhaust emission control catalyst can efficiently remove NO
x
in the exhaust containing a large amount of oxygen, and reduce the amount of particulate matter in the exhaust under high temperature conditions.
In order to solve the above-mentioned problems, a method for controlling the emission of exhaust according to the present invention is characterized by bringing exhaust containing hydrocarbon an
Horiuchi Makoto
Kawanami Makoto
Birch & Stewart Kolasch & Birch, LLP
Dunn Tom
ICT Co., Ltd.
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