In this chapter, a new deNO_x concept by fast reductants injection pulse upstream NSR is introduced. This method has a wider range of applicability for different catalyst temperatures (up to 800 °C) and space velocities than a conventional NO_x storage and reduction system. Various types of mechanism analysis suggest that active intermediate species such as isocyanates (R-NCO) generated from adsorbed NO_x and partial oxidized HCs by fast injection pulse would play a role in high deNO_x performances. The application of the new concept into vehicles will also be considered, in comparison with standard NSR techniques.