Abstract: An exhaust gas catalyst especially for small two-stroke gasoline engines comprises a platinum group metal deposited on a refractory metal honeycomb support and is provided with a diffusion barrier coating which reduces conversion without reducing light-off temperatures. Prolonged catalyst life is shown when exposed to misfire conditions.

Abstract: A system for converting particulate matter in exhaust gases, which system comprises a stoichiometrically-operated engine and an exhaust system including a plasma generator for converting water vapor in the exhaust gases into an oxidant and a filter downstream of the plasma generator. A method for converting particulate matter (PM) in exhaust gases by using plasma-treated water vapor as an oxidant to convert PM trapped on a filter disposed in an exhaust system, and/or to oxidize NO and/or N2 to NO2, in which water vapor, PM, NO and N2 are present in the exhaust gases of a stoichiometrically-operated gasoline engine. The NO2 is then used to combust the PM. Experimentally, the conversion of a gaseous hydrocarbon using a plasma with and without water vapor present can be followed using mass spectrometry.