Development of Three-Way Catalyst with the Simultaneous Function of HC-Trapping and Ni-Free H2S Control

H₂S, which causes the rotten egg odor, has been the one of gaseous components in interest and suppressed by the use of NiO as a scavenger since the start of automotive catalysts application to gasoline emission control in 1970s. Ni-free H₂S suppression has been one of topics in gasoline emission control, because the controversial NiO is not permitted in some regions. It was found that some zeolites had unique H₂S trapping capability from the powder screening works for the alternative H₂S scavenger to NiO.

By combining the well-known property of HC-trapping ability of zeolites, zeolite-containing three-way catalysts were developed to suppress H₂S as well as cold-start HC emission for gasoline engine powered vehicle.

The newly developed catalyst showed equivalent H₂S suppression ability to the conventional NiO-containing catalyst at engine and vehicle test cycles that consisted of sulfur storage and release steps. Zeolite type was selected with respect to H₂S trapping capability and thermal stability. The catalyst containing zeolite decreased the cold-start emissions that were ascribed to the improved HC trapping and TWC performance of the zeolite-containing catalyst.