Chemistry of inorganic compounds – Modifying or removing component of normally gaseous mixture – Mixture is exhaust from internal-combustion engine
Reexamination Certificate
1998-03-02
2001-02-27
Dunn, Tom (Department: 1754)
Chemistry of inorganic compounds
Modifying or removing component of normally gaseous mixture
Mixture is exhaust from internal-combustion engine
C423S213500, C423S239100
Reexamination Certificate
active
06193942
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a catalyst for the decomposition of nitrogen oxides and a method for purifying a diesel engine exhaust gas by the use of the catalyst. More particularly, it relates to a catalyst which is capable of decomposing and allaying particularly nitrogen oxides (NO
x
) among other harmful components in the diesel engine exhaust gas and, at the same time, depriving by combustion the exhaust gas of carbonaceous particulates, unburned hydrocarbons, and carbon monoxide and a method for purifying the diesel engine exhaust gas by the use of this catalyst.
2. Description of the Prior Art
The nitrogen oxides (hereinafter referred to as “NO
x
”) in the diesel engine exhaust gas cause photochemical smog and acidic rain. In recent years, since the emission of the NO
x
from the diesel engines has been posing a social issue particularly in the urban districts, the alleviation of this emission is an important consideration. For this reason, studies aimed at a catalyst for the disposal of the exhaust gas are now under way. Further, since the diesel engine exhaust gas contains particulates harmful to the physical health, the catalyst for the disposal of the exhaust gas of this nature is naturally expected to be capable of decomposing the NO
x
and repressing these particulates as well.
It has been customary heretofore to use a three way catalyst for the purpose of purifying the exhaust gas from an automobile. Since the exhaust gas from a diesel engine excessively contains oxygen, however, the ordinary three way catalyst is incapable of thoroughly allaying the NO
x
.
A catalyst having copper deposited on a porous carrier such as of zeolite, alumina, or silica as disclosed in JP-A-63-100,919, for example, has been available for the removal of the NO
x
from the exhaust gas of a diesel engine or the exhaust gas of a gasoline-lean burn engine which contains oxygen in a large quantity. This catalyst, however, is at a disadvantage in being deficient in resistance to heat and liable to be poisoned by sulfur oxides.
A method for removing the NO
x
by using platinum as a main catalyst in the presence of sulfur oxides has been disclosed, for example, in JP-A-05-137,963. This platinum containing catalyst naturally is highly active in oxidizing SO
2
. When it is used in the disposal of the diesel engine exhaust gas, therefore, it increases sulfate group owing to the oxidation of SO
2
and possibly increases particulates rather than decreases them.
As remarked above, the catalysts heretofore proposed for the removal of nitrogen oxides still have a problem from the practical point of view for the purpose of purifying the exhaust gas from a diesel engine.
It is an object of this invention, therefore, to provide a novel catalyst for the decomposition of nitrogen oxides and a method for purifying the diesel engine exhaust gas by the use of this catalyst.
Another object of this invention is to provide a catalyst which is enabled by the addition of a reducing agent to attain efficient decomposition of the NO
x
in the diesel engine exhaust gas and a method for the use of this catalyst.
Still another object of this invention is to provide a catalyst which effects removal by combustion of such harmful components as unburned hydrocarbons and carbon monoxide, allays particulates, and possesses an ability to withstand elevated temperatures.
SUMMARY OF THE INVENTION
The objects mentioned above are accomplished by a catalyst for the decomposition of nitrogen oxides, having a refractory three-dimensional structure coated with a copper-containing zirconia powder having deposited copper the catalytically active oxide of at least one metal selected from the group consisting of tungsten, gallium, nickel, manganese, iron, and cobalt on a zirconia powder, wherein the zirconia powder has a BET specific surface area in the range of 50 to 200 m
2
/g and an average primary particle diameter in the range of 50 to 200 Å.
This invention further concerns the catalyst for the decomposition of nitrogen oxides, wherein the refractory three-dimensional structure is an open-flow ceramic honeycomb or metal honeycomb. This invention further concerns the catalyst for the decomposition of nitrogen oxides, wherein the copper content as element is in the range of 5 to 50% by weight based on the zirconia powder and in the range of 4 to 100 g per liter of the refractory three-dimensional structure. This invention further concerns the catalyst for the decomposition of nitrogen oxides, wherein the amount of the catalytically active oxide of at least one metal to be used in combination with copper is in the range of 2 to 40% by weight based on the copper element. This invention further concerns the catalyst for the decomposition of nitrogen oxides, wherein the amount of the zirconia powder is in the range of 50 to 250 g per liter of the refractory three-dimensional structure.
The objects mentioned above are also accomplished by a method for the removal of nitrogen oxides in a diesel engine exhaust gas, which comprises exposing to the catalyst the diesel engine exhaust gas whose HC/NO
x
molar ratio is in the range of 0.5 to 20 (HC reduced to methane concentration). The objects are also accomplished by a method for the removal of nitrogen oxides in a diesel engine exhaust gas, which comprises injecting a reducing agent into the diesel engine exhaust gas and exposing the exhaust gas to the catalyst mentioned above.
This invention further concerns the method for the removal of the nitrogen oxides, wherein the temperature of the exhaust gas into which the reducing agent is injected is in the range of 200° to 500° C. This invention further concerns the method for the removal of nitrogen oxides, wherein the reducing agent is gas oil.
The catalytic component of the catalyst according to this invention has the ability to adsorb hydrocarbons which function as a reducing agent for nitrogen oxides. The use of this catalytic component, therefore, enhances the ability of the catalyst to decompose the NO
x
and the ability thereof to purge such substances as unburned hydrocarbons and particulates. To be specific, since the catalyst of this invention has a notable ability to decompose the NO
x
, manifests the effect of repressing particulates, and excels in the ability to withstand elevated temperatures as shown in Table 1, it is useful as a catalyst for purifying the diesel engine exhaust gas.
DESCRIPTION OF THE PREFERRED EMBODIMENT
The catalyst of the present invention for the decomposition of nitrogen oxides is produced by coating a refractory three-dimensional structure with a copper-containing zirconia powder having deposited copper and the catalytically active oxide of at least one metal selected from the group consisting of tungsten, gallium, nickel, manganese, iron, and cobalt on a zirconia powder.
First, the catalytically active oxide to be used in this invention is the oxide of at least one member selected from the group consisting of tungsten, gallium, nickel, manganese, iron, and cobalt, preferably the oxide of iron, tungsten, nickel, or manganese.
This catalytically active oxide is deposited in combination with copper on a zirconia powder to form the copper-containing zirconia powder.
The copper-containing zirconia powder is made to coat the refractory three-dimensional structure.
The copper content as element is in the range of 5 to 50% by weight, preferably 10 to 20% by weight, based on the zirconia powder and in the range of 4 to 100 g, preferably 10 to 40 g, per liter of the refractory three-dimensional structure. If the copper content is less than the lower limit of the range mentioned above, the ability of the catalyst to decompose the NO
x
will be unduly low. Conversely, if the amount of copper to be deposited exceeds the upper limit of the range mentioned above, the excess will bring about no proportionate addition to the ability of the catalyst to decompose the NO
x
and will prove wasteful. As the starting material for the copper, nitrate, sulfate, and other si
Horiuchi Makoto
Okuda Norimasa
Behr, Esq. Omri M.
Dunn Tom
ICT Co., Ltd
LandOfFree
Catalyst for decomposition of nitrogen oxides and method for... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Catalyst for decomposition of nitrogen oxides and method for..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Catalyst for decomposition of nitrogen oxides and method for... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2560923