Abstract: A catalyst reduction system using diesel fuel as a reductant for vehicles equipped with diesel engines reduces NOx transient emissions produced during acceleration. Impending engine accelerations are sensed to produce metered pulse(s) of fuel oil simultaneously with and preferably in advance of, the NOx transient emission. The fuel pulse is sufficient in quantity to reduce the NOx transient emission when the NOx and HC resulting from the cracked fuel oil are present at spatially equal distances within the reducing catalytic converter. Optionally, the washcoat of the reducing catalyst is formulated to delay the adsorption/desorbtion of one of the gases on the washcoat to assure proper timing of the NOx transient and fuel pulse(s).