No abstract

In the practical applications, a high portion of the NO x is emitted without purification in the cold start period of engine because the selective catalytic reduction (SCR) or NO x storage and reduction (NSR) catalysts are not warmed up. Passive NO x absorbers (PNA) were proposed earlier to store the NO x at low temperatures and release the stored NO x during warm-up period when the SCR and NSR catalysts downstream are functional, while this concept just attracted great interests recently to meet the extra stringent requirement of governmental emissions regulations. A plant of PNA catalysts, showing different NO adsorption/release characteristics, was disclosed. This review summarizes the recent progress in the development of PNA catalysts. The characteristics of NO adsorption/release on precious metal (i.e., Pt, Pd) loading Al 2 O 3 support catalysts, CeO 2 support catalysts, and zeolite support catalysts are summarized and compared.