Catalyst – solid sorbent – or support therefor: product or process – Miscellaneous
Patent
1996-05-15
1998-07-14
Wood, Elizabeth D.
Catalyst, solid sorbent, or support therefor: product or process
Miscellaneous
502527, 422180, 261DIG72, B01J 2104, B01D 5000
Patent
active
057803862
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
This invention generally relates to a metal-made support suitable for use in an exhaust gas cleaning system of an automotive vehicle to support thereon an exhaust gas cleaning catalyst.
More specifically, this invention is concerned with an economical metallic support which is excellent in properties such as durability and which features, as constituent members of a metal-made support, use of a cylindrical metal casing, small-diameter open tubes arranged in the metal casing and metal wires fixing the tubes in the metal casing in place of of a costly heat-resistant steel.
BACKGROUND ART
Known catalyst supports of the above-described sort for exhaust gas cleaning systems include two types, one being the ceramic-made monolithic type (ceramic monoliths) and the other the metal-made monolithic type (metallic monoliths).
Especially in recent days, a great deal of research and development work has been concentrated on metallic monoliths with a view to improving drawbacks of ceramic monoliths, in other words, from the view-points of mechanical strength, durability, flow resistance, cleaning efficiency (the size reduction of a system) and the like.
Typical examples of conventional metal-made catalyst supports of this type (MS', metallic supports") are illustrated in FIG. 11 and FIG. 12. A metallic support of this type is constructed of a metallic honeycomb body and a cylindrical metal-made casing 4 opening at opposite ends thereof and fixedly enclosing the metallic honeycomb body therein. In general, the metallic honeycomb body has been fabricated by stacking a planar band 1, which is made of a steel sheet excellent in high-temperature oxidation resistance and heat resistance, and a corrugated band 2, which has been formed by corrugating a similar steel sheet, one over the other in a mutually contiguous relation and then rolling them together into a spiral form or by stacking such planar bands and corrugated bands into a multilayered form, so that the honeycomb body defines a number of network-patterned gas flow passages (cells) for permitting axial passage of exhaust gas therethrough.
Incidentally, FIG. 11 illustrates the rolled metallic honeycomb body H while FIG. 12 depicts the stacked metallic honeycomb body H.
The metallic honeycomb body and the metal-made casing, which make up the above-described metallic support, are then firmly fixedly together by brazing or welding so that they can withstand thermal expansions and thermal stresses--which occur due to the high temperature of exhaust gas itself and an exothermic reaction of the exhaust gas by the cleaning catalyst (a catalyst formed of Pt, Pd, Rh and the like)--and also vibrations during running of the automotive vehicle. Needless to say, the planar band(s) and the corrugated band(s), which form the metallic honeycomb body, are also fixed together at points or areas of contact therebetween by one of various methods.
As the planar band(s) 1 and the corrugated band(s) 2 in each of the above-described conventional honeycomb bodies H, it is possible to use bands (sheets) having a thickness not greater than 0.1 mm and made of a material such as a heat-resistant stainless steel, e.g., chromium steel (chromium content: 13-25%) or Fe--20%Cr--5%Al, or a stainless steel formed by adding one or more rare earth metals to the former stainless steel to improve the high-temperature oxidation resistance. An Al-containing steel band is an extremely preferred material as each band, because it is equipped with improved high-temperature oxidation resistance and, when subjected to heat treatment, .alpha.-Al.sub.2 O.sub.3 is caused to deposit in various forms such as whisker and mushroom forms on its surfaces and serves to firmly hold a wash coat for carrying the exhaust gas cleaning catalyst.
The planar band(s) 1 and corrugated band(s) 2, which make up the metal-made honeycomb body H, are however extremely costly because their material itself is expensive and a rolling cost is needed to form the material into sheets (thickness: 0.04-0.1 mm) suited for this ki
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Hailey Patricia L.
Usui Kokusai Sangyo Kaisha Ltd.
Wood Elizabeth D.
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