New Insights on N2O Formation Pathways during Lean/Rich Cycling of a Commercial Lean NOx Trap Catalyst

Abstract Pathways for N 2 O formation during lean/rich cycling of a commercial LNT catalyst (containing Pt, Pd, Rh as well as Ba, CeZr, MgAl and Al oxides) were investigated based on bench-reactor experiments with spatiotemporally resolved gas measurements (SpaciMS) and in situ surface analysis (DRIFTS). The inlet gas temperature, composition of the rich gas mixture and regeneration length were varied in order to reveal the underlying mechanisms. Particular attention was given to low temperatures where the regeneration was kinetically limited and N 2 O was emitted in two peaks. The primary N 2 O peak appeared immediately after rich-phase inception when platinum-group-metal (PGM) sites over which NO x reduction took place were only partially reduced, and tailed off with the breakthrough of the reductant front. The secondary N 2 O peak appeared at the rich-to-lean transition as a result of reactions between surface-deposited reductive species (NH 3 , CO and/or isocyanates) and residual stored NO x . Therefore, more thorough regeneration (longer rich phase, more efficient reductant, or higher temperature) led to a reduced secondary N 2 O peak. In contrast, CO either produced from reverse water gas shift or injected as a feed could poison PGM sites resulting in self-inhibition of the regeneration and a subsequent significant secondary N 2 O peak.