Abstract: The invention is a nitrogen oxide trap comprising a porous support; and catalysts consisting of manganese and potassium loaded on the porous support. The trap may be used in an internal combustion engine exhaust gas catalyst system. During lean-burn operation of the engine the trap sorbs nitrogen oxides and releases the nitrogen oxides during decreased oxygen concentration in the exhaust gas.

Abstract: The invention is a nitrogen oxide trap comprising a porous support loaded with 6-15 wt. % strontium oxide and thereon, a mixture of: 0.5-5 wt. % precious metal catalyst selected from platinum, palladium, rhodium or mixtures thereof loaded, 3.5-15 wt. % zirconium and 15-30 wt. % sulfate, where preferably the ratio of zirconium to sulfate ranges from about 1:1 to 1:7; each wt. % being individually based on the weight of the support. The trap may be used in an internal combustion engine exhaust gas catalyst system. During lean-burn operation of the engine the trap sorbs nitrogen oxides (NOx) and releases the nitrogen oxides during decreased oxygen concentration in the exhaust gas, the desorbed NOx being converted to N.sub.2 and O.sub.2.

Abstract: The invention is a nitrogen oxide trap separate catalyst phases. One of the phases is platinum on a porous support and another is alkali metal or elements and alkaline earth elements on another porous support. The phases may be provided as an intimate mixture or as layers in the trap. The trap may be used in an internal combustion engine exhaust gas catalyst system. During lean-burn operation of the engine the trap adsorbs nitrogen oxides and releases the nitrogen oxides during decreased oxygen concentration in the exhaust gas.