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The Urea-SCR system has been widely used for the after-treatment of NOx to meet tighter regulations for the heavy-duty diesel engine. In addition, the long useful life time of heavy duty engines requires the highly durable components of urea-SCR system such as the catalyst and urea-dosing unit. This paper focused on the deactivation of the SCR catalyst for the EURO4 engine. The NOx conversion of field-aged catalysts was monitored with certain mileage accumulation at the engine bench and laboratory reactors. The postmortem analysis of the catalysts has been carried out to investigate the possible deactivation routes of SCR catalysts in the real driving condition. The analysis showed that the SCR catalyst was durable enough to meet the legislations over the useful lifetime of the engine and found that the non-thermal mechanisms such as poisoning were major routes for the deactivation of catalysts while the thermal sintering was shown to be marginal.

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.