Modified SCR and SCR/DPF Systems Demonstrate Potential for Reduced NOx and PM in Parametric Tests: The urea SCR system has been well developed to reduce tailpipe NOx emissions in diesel vehicles. The system, however, requires further improvement to improve fuel economy. Namely, the NOx reduction rate needs to be increased under various operating conditions while the system needs to be developed to work well with DPF to reduce PM. A SCR catalyst was developed to improve ammonia adsorption of the catalyst at Nissan Diesel, Waseda University, and Tokyo Roki. Subsequently, two systems for simultaneous reductions of NOx and particulate were evaluated. One system consists of a catalyzed soot filter which is similar to the production system currently used for a diesel truck. The other system was developed to reduce the size of the aftertreatment system. The SCR catalyst was embedded in the substrate material of DPF to reduce the size.