Catalyst – solid sorbent – or support therefor: product or process – Miscellaneous
Patent
1993-11-02
1995-06-20
McFarlane, Anthony
Catalyst, solid sorbent, or support therefor: product or process
Miscellaneous
502527, 148325, 428606, 420 40, 420 62, B01J 2102, B01J 2326
Patent
active
054260841
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to a highly heat-resistant metallic carrier for an automobile catalyst, that can cope with an increase in the temperature of an automobile engine exhaust gas.
BACKGROUND ART
A ceramic honeycomb composed mainly of cordierite has hitherto been used extensively as a carrier for a catalyst for rendering an automobile exhaust pollution-free. In recent years, the advantages of a metallic honeycomb comprising a stainless steel foil have been recognized, and the metallic honeycomb has begun to be mounted on some high grade passenger cars, which has led to an increasing tendency that the number of the metallic honeycombs installed in automobiles has gradually increased. The advantages of the metallic honeycomb include the following: 1 since the temperature rise rate at the start of an engine is higher than that in the case of the ceramic honeycomb, the metallic honeycomb can begin to exhibit catalytic activity for purifying the exhaust gas earlier than the ceramic honeycomb, which contributes to a reduction in the amount of release of toxic gases; 2 since the wall thickness is half or smaller than that of the ceramic honeycomb, the exhaustion resistance becomes so small that the output loss of the engine is small; 3 the surface area per unit volume of the honeycomb is so large that it is possible to relatively reduce the size; and 4 in the ceramic honeycomb, a cushioning material comprising a wire of inconel or a high grade stainless steel should be interposed between the honeycomb and the jacket and, due to poor heat resistance of the cushioning material, there is a limitation on an increase in the temperature of the exhaust gas, whereas the metallic honeycomb is directly joined to the jacket, so that no cushioning material is needed and it can be disposed at a higher temperature portion immediately behind the engine manifold to shorten the build up time of the purification activity of the catalyst.
The metallic honeycomb can be used at a higher temperature than the ceramic honeycomb. In recent years, however, there is an ever-increasing demand for lean burn and high speed running with low fuel consumption against the background of tightening of CAFE and regulation of exhaust gases, which has lead to a tendency of a further increase in the temperature of the exhaust gas from an automobile engine, so that, in some cases, the conventional metallic honeycombs cannot satisfy the new heat resistance requirements.
Specifically, the inlet gas temperature to which the conventional metallic honeycombs have been exposed was about 850.degree. C. at the highest even when they were used immediately behind the engine manifold. In recent years, however, the inlet gas temperature often reaches 900.degree. to 1,000.degree. C. This has made it impossible for the conventional metallic honeycombs to pass a strict test for durability requirements.
For example, as described on pages 70 to 80 of "Nikkei Mekanikaru (Nikkei Mechanical)", No. 20 issued on January in 1992, an improvement in the oxidation resistance of the honeycomb has been considered as the first requirement to be satisfied for improving the heat resistance of the metallic honeycomb. For this reason, as disclosed in, for example, Japanese Unexamined Patent Publication (Kokai) Nos. 92286/1975, 48473/1976 and 71898/1982, attention has been directed to the oxidation resistance of a foil material for a metallic honeycomb and the adhesion of a film, and use has been made of a foil comprising, as a base material, an Fe-Cr-Al-base alloy, which has hitherto been extensively used as a heating wire and a high-temperature member for heaters by virtue of its excellent oxidation resistance and adhesion as a film, and having improved heat resistance or adhesion to an activated alumina (y-Al.sub.2 O.sub.3) coated layer serving directly as a carrier for the catalyst. In all the techniques disclosed in the above-described publications, Y is utilized as means for improving the oxidation resistance of the material.
On the other hand, Japanese
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Fudanoki Fumio
Fukaya Masuhiro
Ohmura Keiichi
Sumitomo Hidehiko
Yamanaka Mikio
McFarlane Anthony
Nippon Steel Corporation
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