SCR for Passenger Car: the Ammonia-Storage Issue on a Fe-ZSM5 Catalyst

A comprehensive experimental approach has been developed for a Fe-ZSM5 micro-porous catalyst, through a collaborative project between IFP, PSA Peugeot-Citroën and the French Environment and Energy Management Agency (ADEME). Tests have first been conducted on a synthetic gas bench and yielded estimated values for the amount of NH₃ stored on a catalyst sample. These data have further been compared to those obtained from an engine test bench, in running conditions representative of the entire operating range of the engine. 15 operating points have been chosen, considering the air mass flow and the exhaust temperature, and tested with different NH₃/NOx ratios. Steady-state as well as transient conditions have been studied, showing the influence of three main parameters on the reductant storage characteristics: exhaust temperature, NO₂/NOx ratio, and air mass flow. It has also been shown that the reducing agent release strongly depends on the current exhaust conditions, but also on the way it has been stored. From this knowledge, an optimized NEDC cycle was developed, leading to a large NOx abatement matching Euro 6 standards.