NOx storage-reduction catalyst for automotive exhaust with improved tolerance against sulfur poisoning

Role of Support in Lean DeNOxCatalysis

“…The influence of the support on the stability of BaCO 3 decomposition of barium nitrate formed during NO x storage indicated that only 30% of the loaded Ba is involved in the NO x storage process.…”

“…In figure 3 3 . Band 3000 -3750 cm )1 is due to OH-groups and therefore is related to evolution of water.…”

“…The catalysts after exposure to NO pulses in 5% O 2 / He at 300°C were analyzed by DRIFT-spectroscopy (figure 6(a) and 6(b)). Al 2 O 3 and Pt/Al 2 O 3 samples ( figure 6(a)) contained carbonate species of various types (bands at 1300-1600 cm )1 ), whereas Ba containing samples showed bands characteristic for bulk BaCO 3 (1:1 KBr diluted, figure 6(a) dotted lines). After NO + O 2 exposure at 300°C, the Ba containing samples showed absorbance bands matching those of bulk Ba(NO 3 ) 2 (1:1 KBr diluted, figure 6(b) (Al + NO ) ) and to nitrates (Al + NO 3 ) ) species, respectively [8].…”

“…In 1996, Takahashi et al [2] proposed a storage mechanism in which NO is oxidized on Pt to NO 2 , then stored as Ba(NO 3 ) 2 and subsequently reduced by HC activated on Pt sites. The primary role of Ba as storage compound was shown in [3][4][5], whereas some debate is still open about the kind and amount of Ba containing species active during NO x storage. Applying TPD on activated catalysts Prinetto et al [5] estimated that 50% of Ba is present as BaCO 3 which is subsequently decomposed by the formation of bulk Ba(NO 3 ) 2 .…”

Multifunctional catalyst for maximizing NOx oxidation/storage/reduction: The role of the different active sites

“…The combination of basicity and redox properties is the basis of the NO x storage-reduction (NSR) catalysts [18][19][20]. These catalysts store the NO x as nitrates on lean (oxidizing) conditions and reduce the stored nitrates under the rich (reducing) conditions.…”