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Low cost and S(sulphur)-tolerant DOCs (Diesel Oxidation Catalysts) are being demanded in emerging countries such as China and India, where Euro 4 and 5 type emission standards are going to be implemented or are being implemented. However, fuel S content is different in the metros vis-à-vis non metros in many emerging countries. In such a scenario, DOCs need to maintain catalytic performance with high S fuel as well as standard low S fuel. This paper describes the development results of S tolerant Pt-Pd based DOCs. A new washcoat technology (WT D) has been developed for EU 4 passive Pt-Pd DOC applications, in which PGM cost was thrifted by replacing part of Pt by Pd. Vehicle test results after thermal ageing and S poisoning demonstrated that the Pt-Pd DOC (Pt:Pd=4:1) prepared with WT D gave similar tailpipe CO (Carbon monoxide) and HC (Hydrocarbon) emission conversions as a commercially available EU 4 passive Pt-only DOC when 50ppm S diesel fuel was used.

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.