Method for converting exhaust gases from a diesel engine using nitrogen oxide absorbent

A method for treating exhaust gases generated by a diesel engine, said method comprising the steps of:

• locating in an exhaust gas passage of a diesel engine a first catalyst component comprising a nitrogen oxide absorbent material capable of absorbing nitrogen oxides at low temperatures and a second catalyst component downstream of said first catalyst component comprising a lean-NOx catalyst or selective reduction catalyst, said nitrogen oxide absorbent material consisting essentially of:
• (a) a porous support material of alumina, and
• (b) at least 0.1 wt. % precious metal based on the weight of the porous support material selected from the group consisting of platinum, palladium, and rhodium, or a mixture of any of them;
• exposing said first catalyst component to oxidizing diesel exhaust gases, where at low temperatures nitrogen oxides are absorbed from the exhaust gas by said porous support material through the catalytic effect of said precious metal and at higher temperatures are desorbed and passed to the second catalyst component where the nitrogen oxides are reduced to nitrogen or nitrous oxide.