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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.

It is well known that two representative methods satisfy the EURO4 emission regulation. The one is the EGR system that reduces NOx by using EGR (Exhaust Gas Recirculation) and eliminates PM (Particulate Matter) by DPF (Diesel Particulate Filter). But this system has disadvantages of fuel efficiency and requirement for larger engine cooling capacity. The other is SCR (Selective Catalyst Reduction) system that reduces NOx by dosing reagent into exhaust gas. The SCR system also needs to decrease PM by optimization of combustion. The SCR system has advantages of fuel economy and good engine durability. As the price of oil goes up, the commercial vehicle drivers are more concerned about the fuel economy lately, so the European major manufacturer of commercial vehicle adopted the SCR system because of above mentioned advantages. This paper focused on the development of EURO4 engine and commercial vehicle equipped with SCR system.