Enhanced methane conversion under periodic operation over a Pd/Rh based TWC in the exhausts from NGVs

Journal article, 2013

The enhancement of methane oxidation performances under periodic operation over a commercial Pd–Rh based three way catalyst (TWC) is investigated at different temperatures. Results confirm that under conditions with periodic oscillating feed around stoichiometry (λ = 1 ± 0.02), higher and more stable CH4 conversion are obtained than under conditions with constant stoichiometric feed. In particular higher CH4 conversion is obtained in the rich part of the cycle than in the lean one, the difference being more pronounced at high temperature. A narrow turning point for the TWC activity is finally observed under slightly rich conditions, which is characterised by a marked increase of CH4 conversion, paralleled by total consumption of O2 and NO and formation of small amounts of CO, H2 and NH3. Results suggest that the oxidation state of palladium plays a key role in the observed enhancement of catalyst performances.