Impact of gas phase reactions and catalyst poisons on the NH3-SCR activity of a V2O5-WO3/TiO2 catalyst at pre-turbine position

With stricter regulations and decreasing exhaust gas temperature due to more efficient engine management, NOx abatement remains a critical issue despite many technical and catalytic advances. To counterbalance these challenges the positioning of exhaust gas aftertreatment systems in front of the turbocharger has gained significant interest in recent years. In this context, we report a systematic study on the impact of propylene, ndodecane, and o-xylene as well as of SO2 on the gas phase reactions and NH3-SCR activity of a conventional vanadium-based catalyst at increased pressure. An elevated pressure is shown to dramatically promote homogeneous reactions of hydrocarbons, which subsequently contribute to an increased NO oxidation but also to parasitic NH3 overconsumption. The hydrocarbons are also faster catalytically oxidized and affect NOx reduction at all investigated temperatures. Their presence in the exhaust gas further leads to the formation of the toxic byproducts HCHO and HCN. Upon short term exposure to 20 ppm SO2 in the feed gas, no significant catalyst poisoning was observed. However, for longer exposure times an enhanced formation of sulfur containing deposits was encountered at low temperatures for elevated pressures. Notably, their poisonous effect was reversible after heating to high temperatures.