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

A nanocomposite of Al sub(2)O sub(3) and ZrO sub(2)-TiO sub(2) solid solution (AZT) was synthesized for NO sub()xstorage-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 sub()xstorage capacity after thermal aging. This enhanced storage capacity was attributed to the fact that ZrO sub(2)-TiO sub(2) solid solution (ZT) was crystallized and stabilized. The solid-state reaction of potassium, which was added as a NO sub()xstorage material, was inhibited in the AZT catalyst, relative to those containing AZT calcined at a low temperature. The AZT catalyst also showed excellent NO sub()xstorage performance after sulfur aging at 973 K or higher, compared with the catalyst containing physically mixed Al sub(2)O sub(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 sub()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.