Study On The Preparation And Perofances Of NO_x Storage-reduction Catalyst Pt/Ba/TiCeO

Increasingly stringent environmental regulations for diesel engines and the automotive industry's shift toward lean-burn gasoline engines provide the impetus for new approaches to NO_X emission control. While conventional three-way exhaust catalysts are ineffective under lean-burn conditions, reducing NO_X emissions under lean (oxygen-rich) conditions requires new catalytic technology. The NO_X storage reduction (NSR) catalyst is one promising candidate. The prototypical NSR catalyst, Pt/BaO/Al₂O₃, consists of Pt and BaO dispersed on a high-surface-area alumina support. The commercial viability of NSR catalysts is limited by the narrow range of operating temperatures, thermal degradation and deactivation by sulfur adsorption. This paper describes the preparation, characterization and testing of a NSR catalyst consisting of Pt and Ba dispersed on a strongly basic titanium- cerium oxide (TiCeO) support that also functions as a NO_X adsorbent. The properties of catalysts were evaluated by XRD, BET and TPD, meanwhile, their catalytic activities were evaluated by performing NO_X isothermal storage experiments and dynamic storage-reduction.The results of NO_X isothermal storage experiments indicate that TiCeO bi-oxide in Pt/Ba/TiCeO catalyst exhibited as both a support and an storage component in the NO_X storage-reduction process. Pt and TiCeO can catalyze the oxidation of NO, resulting in much higher NO_X storage capacity. The addition of Ba-loading (6%) also had a significant increase of NO_X storage capacity. In particular, the storage of NO_X on the Pt/Ba/TiCeO catalyst proceeds very efficiently even at low temperatures (150℃). At 350℃, after 10 times NO_X Storage-Reduction cycles, NO_X storage capacity of Pt/BaO/TiCeO is no less than 317μmol/g, and the selectivity of H₂ reducing nitrate to N₂ is higher than 93%. The results of TPD analysis indicate that during low-temperature storage process, lots of surface species such as physically adsorbed species, weakly chemisorbed species were formed by NO sorption; while mainly nitrates were formed by NO_X sorption after NO oxidation during high-temperature storage process. When 200ppm SO₂ was added to the reaction feed, loss of NO_X storage capacity has being founded, with the result of a suppression of SO_X adsorption.Based on the experimental results, a mechanism of NO_X storage process has been proposed.