Short Pulse Reductive Activation of Pt/ceria for the Low-Temperature CO Abatement in Vehicles Operated with the Synthetic Diesel Fuel OME

Abstract

The synthetic Diesel fuel oxymethylene ether (OME) is sulfur-free by nature, and due to the low soot formation, no active filter regeneration events are required, limiting the maximum temperatures seen by the exhaust catalysts to ~ 450 °C. These OME-specific ageing requirements will enable the application of new types of catalysts that cannot be used in conventional Diesel vehicles. Such new catalytic solutions will allow ultra-low emissions at a much-reduced cost and will hence contribute to the overall efficiency of the OME approach. In this contribution, we focus on CO abatement from OME exhaust. To enable an efficient evaluation of new catalysts under practically relevant conditions, a test bench was set up that can reproduce the transient temperature-, mass flow- and concentration profiles measured during real driving tests. In a first step, the transient test bench was used to compare CO oxidation over a commercial Diesel oxidation catalyst for OME- and conventional Diesel conditions. The same low-load cold-start drive cycle run with OME showed slightly lower raw emissions, but the CO emissions downstream of the catalyst increased by a factor of ~ 2. The main reason for the lower CO conversion is the lower temperature of the OME exhaust. In a second step, we investigated short-pulse reductive activation of Pt/ceria as a promising new technology that benefits from the OME-specific low ageing requirements. A Pt/ceria catalyst activated by a short 5–10 s reductive pulse achieved virtually 100% conversion even at exhaust temperatures below 80 °C. With one 5 s reductive activation pulse per 30-minute drive cycle, a CO conversion of > 99.9% is demonstrated over the low-load cold-start OME drive cycle, compared to 59% obtained with a standard commercial Diesel oxidation catalyst. To our knowledge, this is the first published demonstration of short pulse reductive activation of Pt/ceria for CO oxidation using realistic transient drive cycles.