Regeneration mechanism of Pt/BaO/Al2O3 lean NOx trap catalyst with H2

✍ Scribed by S.S. Mulla; S.S. Chaugule; A. Yezerets; N.W. Currier; W.N. Delgass; F.H. Ribeiro

• Publisher: Elsevier Science
• Year: 2008
• Tongue: English
• Weight: 1018 KB
• Volume: 136
• Category: Article
• ISSN: 0920-5861
• DOI: 10.1016/j.cattod.2008.01.007

✦ Synopsis

Regeneration of a Pt/BaO/Al 2 O 3 NO x storage-reduction catalyst was studied using H 2 as a model reductant. We propose that the regeneration process involves a localized reaction front of the reductant that travels through the catalyst bed with complete regeneration of the trapping sites. When NH 3 was used as a regenerating gas instead of H 2 , the process was found to be equivalent to that with H 2 , and NH 3 was found to be as effective as H 2 in regenerating the trap catalyst. The process was limited only by the supply of the hydrogen atoms, irrespective of the source of hydrogen (H 2 or NH 3 ) and was also not affected by temperature changes or by the presence of CO 2 and H 2 O. Even though Pt by itself is not very selective in reducing the NO x to N 2 in a NO x /H 2 feed stream, a high N 2 selectivity is maintained over the Ba-containing trap catalyst since the undesirable byproducts, mainly NH 3 , continue to react further until they are optimally converted to N 2 . In fact, we propose that the regeneration of the trap catalyst using H 2 as the reductant involves the formation of NH 3 as an intermediate from the stored NO x , and NH 3 acts as a carrier of Hatoms. The NH 3 ultimately gets further oxidized to N 2 by the stored NO x , the oxygen source on the catalyst, giving high selectivity towards N 2 .