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This paper presents a new substrate for Lean NOx Traps (LNT) which enables high NOx conversion efficiency, even after long-term aging, when using alkali metals as the NOx adsorber. When a conventional metal honeycomb is used as the LNT substrate, the chromium in the metal substrate migrates into the washcoat and reacts with the alkali metals after thermal aging. In order to help prevent this migration, we have developed a new substrate where a fine -alumina barrier is precipitated to the surface of the metal substrate. The new substrate is highly capable of preventing migration of chromium into the washcoat and greatly enhances the NOx conversion. The durability of the new substrate and emission test using a test vehicle are also examined.

As a result of higher exhaust gas temperature for an improvement of fuel consumption, catalytic converters must be much more durable at high temperature. To satisfy such requirements, we have developed an advanced metal substrate using newly developed stainless Fe-Cr-Al foil, which contains more than 7.5 mass% of aluminum. The developed foil elongates durable lifetime about 4 times compared with the conventional foils in high temperature oxidizing atmospheres. The newly developed metal substrate is suitable for exhaust systems which is used under conditions of high exhaust gas temperature above 1000 °C.