Catalyst – solid sorbent – or support therefor: product or process – Catalyst or precursor therefor – Sulfur or compound containing same
Reexamination Certificate
2002-05-06
2004-02-24
Wood, Elizabeth D. (Department: 1755)
Catalyst, solid sorbent, or support therefor: product or process
Catalyst or precursor therefor
Sulfur or compound containing same
C502S222000, C502S223000, C502S219000, C502S527150, C502S527160
Reexamination Certificate
active
06696386
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to an exhaust gas purification catalyst for purification of exhaust gases by burning particulates (solid carbon fine particles, liquid or solid high molecular weight hydrocarbon fine particles; hereinafter sometimes referred to as “PM”) contained in exhaust gases discharged from diesel engines, and exhaust gas purification materials using the catalyst.
BACKGROUND OF THE INVENTION
Recently, it has become clear that particulates discharged from diesel engines are mostly less than 1 micron in their particle diameter and are apt to float in the atmosphere and readily taken into human bodies by breathing, and, besides, they contain carcinogenic substances such as benzpyrene. Thus, their effects on the human bodies have become serious. Under the circumstances, regulations against discharging of particulates from diesel engines are further tightened, and exhaust gas purification catalysts and exhaust gas purification materials which are capable of efficiently removing the particulates.
Hitherto, as one of the methods for the removal of particulates from exhaust gases, there is a method which comprises collecting particulates in exhaust gases using a heat resistant exhaust gas purification material having a three-dimensional structure, heating the exhaust gas purification material by a heating means such as a burner or an electric heater after rising of the back pressure, thereby burning the deposited particulates to convert them to carbon dioxide, and discharging the carbon dioxide to the outside.
However, the above method suffers from the problem that since the burning temperature of the particulates is high, a large energy is required for burning and removing the collected particulates and regenerating the filters. Further problem is that the filters undergo melting loss or cracking owing to the burning in a high temperature region and the reaction heat generated therein. Another problem is that the size of the purification apparatuses becomes large and the cost increases because special devices are required.
On the other hand, there are methods according to which the fine particles are subjected to burning reaction by the catalytic action of catalysts, thereby to perform burning and regeneration in the exhaust gas at the temperature of the exhaust gas without using heating means such as heaters.
As an exhaust gas purification material which supports a catalyst, there is a material which comprises a heat resistant three-dimensional structural body on which an exhaust gas purification catalyst is supported, and the particulates collected therein can be burnt at lower temperatures by the catalytic action of the exhaust gas purification catalyst.
If particulates can be burnt at the exhaust gas temperature using the above exhaust gas purification material having an exhaust gas purification catalyst supported thereon, there is no need to provide a heating means in an exhaust gas purification apparatus, and, thus, construction of the exhaust gas purification apparatuses can be simplified.
However, at present, for the exhaust gas purification materials on which an exhaust gas purification catalyst is supported, it is still difficult to burn sufficiently the particulates at the exhaust gas temperature, and a heating means must be used in combination. Accordingly, there has been desired development of exhaust gas purification catalysts on which is supported an exhaust gas purification materials having such a high catalytic activity as being capable of burning the particulates at lower temperatures.
As exhaust gas purification catalysts, those which contain oxides of metals such as copper and vanadium have been known to have relatively high activity.
For example, JP-A-58-143840 discloses “a particulate purification catalyst comprising a combination of at least one member selected from copper and compounds thereof and at least one member selected from metals and compounds thereof capable of having a plurality of oxidation states”, and JP-A-58-174236 discloses “a catalyst for purification of particulates contained in exhaust gases which comprises at least one member selected from vanadium and vanadium compounds”.
However, the exhaust gas purification catalysts disclosed in these patent publications have the problem that since the catalytic activity of the exhaust gas purification catalysts is not so high as capable of sufficiently burning the particulates at low temperatures of the exhaust gas temperatures, the particulates collected in the exhaust gas purification materials cannot be burnt at the exhaust gas temperatures, and, thus, a heating means must be used in combination.
Furthermore, JP-B-4-42063 discloses “an exhaust gas purification catalyst comprising a metal oxide such as of copper, manganese or molybdenum to which an alkali metal oxide and a noble metal are added, and a method for producing the same”.
However, the exhaust gas purification catalyst disclosed in the above patent publication has the problem that the catalyst has an alkali metal oxide as a component, and the alkali metal oxide is inferior in heat resistance and is scattered by the heat of the exhaust gas or reacts with other catalyst components. Moreover, the exhaust gas purification catalyst has another problem that it is poisoned with sulfur oxide contained in the exhaust gas to cause deterioration of catalyst activity.
The present invention solves these problems encountered with the conventional techniques, and the object of the present invention is to provide an exhaust gas purification catalyst which has a high catalytic activity for burning of particulates, can exhibit sufficiently the respective catalytic characteristics, can sufficiently burn and remove particulates at a temperature close to the exhaust gas temperature, and is high in exhaust gas purification efficiency, and an exhaust gas purification material which can burn and remove particulates at a very high efficiency and is considerably excellent in endurance and economical efficiency.
SUMMARY OF THE INVENTION
The exhaust gas purification catalyst of the present invention for the solution of the above problems has a construction which contains a first catalyst component comprising an inorganic oxide having heat resistance and a transition metal oxide supported on the inorganic oxide and a second catalyst component comprising at least one alkali metal sulfate.
By allowing the catalysts having different functions to be separately present as mentioned above, their different catalytic characteristics can be sufficiently brought out and, furthermore, deterioration caused by reaction between the catalysts per se can be inhibited, and, as a result, deterioration of activity of the catalyst can be inhibited, whereby an exhaust gas purification catalyst of high activity can be obtained.
Moreover, by forming a catalyst component on the surface of a heat resistant inorganic oxide, the surface area of the catalyst increases, and thus the contact points with the particulates in the diesel exhaust gas increase. As a result, an exhaust gas purification catalyst of high activity can be obtained.
DETAILED DESCRIPTION OF THE INVENTION
The exhaust gas purification catalyst of the present invention contains a first catalyst component comprising an inorganic oxide having heat resistance and a transition metal oxide supported on the inorganic oxide and a second catalyst component comprising at least one alkali metal sulfate. That is, the catalysts having different functions are separately provided, whereby their respective different catalytic characteristics can be sufficiently brought out, deterioration caused by reaction between the catalysts per se can be inhibited, thus deterioration of activity of the catalyst can be inhibited, and, as a result, an exhaust gas purification catalyst of high activity can be obtained.
Moreover, a catalyst component is formed on the surface of an inorganic oxide having heat resistance, whereby the surface area of the catalyst increases, thus the contact points with the particulates in th
Arita Masaaki
Hashimoto Yota
Inoue Masahiro
Miyazaki Tatsuro
Tokubuchi Nobuyuki
Hailey Patricia L.
Matsushita Electric - Industrial Co., Ltd.
Stevens Davis Miller & Mosher LLP
Wood Elizabeth D.
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