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A new state of the art DOC (Diesel Oxidation Catalyst) having superior light-off and exothermic activity for forced regeneration compared to conventional Pt base passive DOC, was investigated for LDD application. The DOC uses the latest Pt/Pd technology resulting cost effective DPF system. The newly developed DOC demonstrated improved catalytic activities from Pt only DOC in model gas or engine bench tests. In this study, DOC at early development stage showed excellent light-off activity in model gas and engine bench test compared to conventional Pt only DOC, however, it showed “extinction” phenomenon which is one of the deactivation mode while the post injection and it was observed when post injection operation was done at lower DOC inlet temperatures, e.g. below 250 C. Temperature profiles along diameter and length into DOC bed while active regeneration suggested extinction would be caused by fouling of supplied hydrocarbons derived from diesel fuel.

Two-brick (tandem) three-way underfloor catalyst systems provide greater emission reduction performance compared to comparable single brick TWC systems, which contain the same amount of platinum group metal (PGM) for the same catalyst volume. This superior emission reduction performance is speculated to be due to front catalyst activity promoted by heat transfer from reverse exhaust gas flow in the gap between the front and the rear catalyst of tandem TWC system (hereinafter, tandem gap). Furthermore, the following findings were obtained by conducting experiments with model catalysts. 1) During catalyst light-off phase, conversion efficiency strongly depends on activity of the front portion of catalyst where temperature rises rapidly.