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. When 350ppm S fuel was used, the Pt-Pd DOC exhibits higher CO and THC emission conversions than the Pt DOC.
For EU 5 pre-DPF (Diesel Particulate Filter) DOC, a new washcoat technology (WT E) has been proposed. Engine bench test results show the DOC prepared with WT E has higher CO and HC oxidation activity than a commercially available EU 5 Pt-Pd DOC (WT B) after S poisoning and 40∼50% PGM cost can be thrifted. Moreover, fuel combustion performance for downstream CSF (catalyzed soot filter) at forced regeneration has been proven, even with 500 ppm S fuel.
