Abstract: This method comprises bringing exhaust gas from an internal combustion engine, which is operated at a fuel-lean air/fuel ratio, in contact with an iridium-containing catalyst in a first zone and then in contact with a platinum-containing catalyst in a second zone situated downstream of the first zone. This method is effective for exhaust gas from lean burn engines over a wide temperature range of 200 to 500.degree. C., produces less N.sub.2 O in a low-temperature range of 200 to 300.degree. C., and can purify exhaust gas stably and effectively even at a high temperature of 700.degree. C. or over.

Abstract: The present invention provides a catalyst and method for purifying exhaust gases, having superior performance of NOx purification to exhaust gases containing oxygen and nitrogen oxides, particularly superior performance of NOx elimination to exhaust gases from lean-bum engines with excess oxygen, and a wider effective temperature range of NOx elimination, and also superior heat resistance at high temperature, said catalyst for purifying exhaust gases comprises, as indispensable contents, iridium and alkaline metal loaded on a carrier which is at least one selected from metal carbide and metal nitride, or these and at least one element selected from the group consisting of alkaline earth metal elements and rare earth metal elements, and said method using these catalyst.

Abstract: A NO.sub.x removal catalyst resistant to high temperatures, comprising an activated alumina wherein the specific surface area measured by the nitrogen adsorption method is 120 m.sup.2 /g or more, the bulk density measured by the mercury porosimetry is 0.60 g/cm.sup.3 or more, and the skeleton density measured by the mercury porosimetry is 1.80 g/cm.sup.3 or less and silver carried on said activated alumina. Then said catalyst or a structure having said catalyst coated on a substrate is brought in contact with exhaust gas from an internal combustion engine that is operated at a lean fuel/air ratio, such as a lean-burn engine, NO.sub.x can be removed efficiently within a quite short contact time.

Abstract: A NO.sub.x removal catalyst resistant to high temperatures, comprising an activated alumina wherein the specific surface area measured by the nitrogen adsorption method is 120 m.sup.2 /g or more, the bulk density measured by the mercury porosimetry is 0.60 g/cm.sup.3 or more, and the skeleton density measured by the mercury porosimetry is 1.80 g/cm.sup.3 or less and silver carried on said activated alumina. When said catalyst or a structure having said catalyst coated on a substrate is brought in contact with exhaust gas from an internal combustion engine that is operated at a lean fuel/air ratio, such as a lean-burn engine, NO.sub.x can be removed efficiently within a quite short contact time.

Abstract: A catalyst comprising an iridium supported on at least one carrier selected from the group consisting of metal carbides and metal nitrides for eliminating nitrogen oxides in exhaust gas in the presence of oxygen in excess of the stoichiometric quantity of oxidizing components for reducing components. The catalyst is effective for eliminating NO.sub.x in exhaust gas from lean burn engines such as lean burn gasoline engines and diesel engines containing excess O.sub.2 corresponding to an A/F ratio of 17 or over.

Abstract: A catalyst comprising an iridium supported on at least one carrier selected from the group consisting of metal carbides and metal nitrides for eliminating nitrogen oxides in exhaust gas in the presence of oxygen in excess of the stoichiometric quantity of oxidizing components for reducing components. The catalyst is effective for eliminating NO.sub.x in exhaust gas from lean burn engines such as lean burn gasoline engines and diesel engines containing excess O.sub.2 corresponding to an A/F ratio of 17 or over.

Abstract: There is described a catalyst for purification of exhaust gases containing nitrogen oxides wherein oxygen is co-existent in excess of a stoichiometric amount, characterized in that a coprecipitated mixed oxide of copper and tin is loaded on a carrier composed of at least one type selected from the group consisting of crystalline aluminosilicate, aluminogallosilicate and gallosilicate, or the coprecipitated mixed oxide of copper and tin and further at least one noble metal selected from the group consisting of platinum, palladium, rhodium, iridium, ruthenium, silver and gold are co-loaded thereon.This invention provides a lean NOx purification catalyst having high NOx purification performance and markedly increased durability over a wide temperature range.