In the NOx adsorber/selective catalytic reduction (SCR) combination double layer system, lean NOx is adsorbed on a ceria material. During rich operation some of the NOx is converted to ammonia which is stored and used during lean operation on an upper platinum SCR catalyst (31) (Courtesy of ika and VKA Aachen Kolloquium; and Honda); OSC = oxygen storage capacity; ad. = adsorbed