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Category: Emissions Control
Subject: Methane exhaust reduction for Euro 5
Under the current standards, are palladium catalysts efficient enough under working conditions, to be used in catalytic converters for natural gas fuelled vehicles? Or, would the palladium be so poisoned by sulfur and/or methane emissions that only platinum itself can be used in this application?
Light vehicles using LPG would use the same catalysts as those running on gasoline. CNG is a little different because methane, the majority component of CNG, is a very stable molecule and is harder to oxidise than the higher chain hydrocarbons present in gasoline. Therefore although light duty CNG vehicles in Europe use gasoline-type palladium-rhodium three-way catalyst (TWC) technology, the Pd loading tends to be higher than on gasoline to achieve light-off.
I believe that the sulfur content of CNG fuel is comparable to gasoline (less than 10 ppm) - in any case the level of S is not a problem for Pd.
Answer posted 30th May 2012
Answered by: Dr Lucy Bloxham
Affiliation: Affiliation: Senior Market Analyst, Johnson Matthey Plc