Die Abgasreinigung der FSI-Motoren von Volkswagen

Formation and stability of barium aluminate and cerate in NOx storage-reduction catalysts

“…The introduction of lean-burn engines with direct fuel injection is presently one of the most promising engine concepts to decrease fuel consumption [1][2][3]. The lean-burn engines, which operate at air-fuel ratios higher than 25:1, thus contribute to the conservation of fossil fuel reserves and thereby reduce the associated CO 2 emission.…”

“…Among the different strategies to reduce NO x -emissions, the NO x storage-reduction (NSR) catalyst system is wellestablished because of its high lean DeNO x activity combined with a suitable durability and three-way catalyst activity [2,5,6].…”

“…NSR catalysts consist of precious metals (Pt, Rh) for the oxidation of NO to NO 2 (under lean fuel conditions) and reduction of NO x (under rich conditions), and of a storage component deposited on carrier oxides with a high surface area, such as La 2 O 3 -stabilized γ-Al 2 O 3 or CeO 2 [5][6][7][8][9][10]. Typical NO x storage compounds are alkali metal oxides or alkaline-earth metal oxides like potassium oxide or barium oxide.…”

“…Deactivation of NSR catalysts is mainly caused by sulfur and thermal deterioration. Apart from the development of catalysts with higher tolerance of SO 2 or SO 2 -derived species [11,12], one of the major challenges is therefore the improvement of the thermal stability of NSR catalysts under operating conditions. Thermal deterioration occurs both due to the particle growth of the precious metals and due to the formation of mixed oxides such as aluminates, cerates, and zirconates by the reaction of NO x storage material with the support or compounds in the wash-coat [8,[13][14][15][16].…”

“…In contrast, relatively little attention has been given to studies on the reaction of the storage material with the support during ageing and the stability of the formed phases in the presence of NO x , CO 2 , and H 2 O containing gases.…”