Abstract: The invention is a nitrogen oxide trap comprising a porous support of alumina; and loaded thereon materials consisting essentially of particular amounts of: (I) tungstophosphoric acid and (II) precious metal selected from platinum, palladium, rhodium and mixtures thereof. The trap is useful for trapping nitrogen oxides produced in the exhaust gas generated by an internal combustion gasoline engine during lean-burn operation of the engine. The trap releases the nitrogen oxides during decreased oxygen concentration in the exhaust gas. The desorbed NOx may be converted over the precious metal to N.sub.2 and O.sub.2 by reductants like hydrocarbons present in the exhaust gas.

Abstract: The invention is a method for treating exhaust gases generated by a diesel engine by providing a sulfur-tolerant lean-NOx catalyst in an exhaust gas passage of the engine and contacting the catalyst with the exhaust gases. The sulfur-tolerant lean-NOx catalyst comprises a support of titania aerogel; and loaded thereon, using impregnation techniques from a solution of their precursors, at least 0.25 weight percent precious metal selected from platinum, palladium, rhodium, or mixtures thereof. The method converts the hydrocarbons, carbon monoxide and nitrogen oxides into more desirable gases. In particular, the NOx is converted to N.sub.2 and O.sub.2 over the catalyst.