Improved NO(x) storage-reduction catalysts using Al(2)O(3) and ZrO(2)-TiO(2) nanocomposite support for thermal stability and sulfur durability

A nanocomposite of Al(2)O(3) and ZrO(2)-TiO(2) solid solution (AZT) was synthesized for NO(x) storage-reduction (NSR) catalysts Pt/Rh/Ba/K/AZT, and the effect of calcination temperature on thermal stability was investigated. The catalyst containing AZT calcined at 1073 K (AZT catalyst) had a high NO(x) storage capacity after thermal aging. This enhanced storage capacity was attributed to the fact that ZrO(2)-TiO(2) solid solution (ZT) was crystallized and stabilized. The solid-state reaction of potassium, which was added as a NO(x) storage material, was inhibited in the AZT catalyst, relative to those containing AZT calcined at a low temperature. The AZT catalyst also showed excellent NO(x) storage performance after sulfur aging at 973 K or higher, compared with the catalyst containing physically mixed Al(2)O(3) and ZT (physically mixed catalyst). Furthermore, AZT catalysts inhibited the solid phase reaction of potassium with support materials and kept a high ratio of active potassium, which can store NO(x). Further, because the barium in the AZT catalyst prevented sulfur poisoning, the ratio of active barium in the AZT catalyst was also larger than that in the physically mixed catalyst, probably because of the low basicity and high Pt dispersion of AZT.