Improved NO(x) Storage/Release Properties of Ceria-Based Lean NO(x) Trap Compositions with MnO(x) Modification

Ceria/spinel-based lean NO(x) trap compositions with and without barium were modified with MnO(x) via incipient wetness impregnation. The effect of the MnO(x) layer on the aged materials (850 °C) as to the NO(x) storage and release properties was investigated via NO(x) adsorption (500 ppm NO/5% O(2)/balance N(2)) carried out at 300 °C in a dual-bed with a 1% Pt/Al(2)O(3) catalyst placed upstream of the samples to generate sufficient amounts of NO(2) required for efficient NO(x) storage. Subsequent temperature programmed desorption (TPD) experiments were carried out under N(2) from 300 °C to 700 °C. The addition of MnO(x) to the barium free composition led to a slightly reduced NO(x) storage capacity but all of the ad-NO(x) species were released from this material at significantly lower temperatures (ΔT ≈ 100 °C). The formation of a MnO(x) layer between ceria/spinel and barium had a remarkable effect on ageing stability as the formation of BaAl(2)O(4) was suppressed in favour of BaMnO(3). The presence of this phase resulted in an increased NO(x) storage capacity and lower desorption temperatures. Furthermore, NO(x) adsorption experiments carried out in absence of the Pt-catalyst also revealed an unexpected high NO(x) storage ability at low NO(2)/NO ratios, which could make this composition suitable for various lean NO(x) trap catalysts (LNT) related applications.