NOx storage and reduction in lean burn vehicle emission control: a catalytic engineer's playground

The reduction of NOx (NO + NO2) in lean burn vehicle exhaust is the latest challenge for catalytic engineers to meet increasingly stringent emissions standards. The lean NOx trap (LNT) is an adsorptive catalytic reactor in which NOx is stored as nitrates in excess O2 and then reduced during a brief regeneration. The multi-functional Pt-based LNT catalyst must carry out NO oxidation, NOx storage, and NOx reduction, all within a 1–2 min cycle and achieve >95% NOx conversion. This review describes studies of the transient coupling between reaction and transport, and links between catalyst composition, structure, NOx conversion, and selectivity to N2 and NH3. A glimpse is offered of emerging lean NOx reduction technologies and the new challenges they pose.

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► NOx storage and reduction is emerging method for abating NOx from lean burn vehicles, sustaining the tradition of coupling storage with catalysis.
► The NSR catalyst performs several functions during a 1–2 min cycle: oxidation, storage, reduction, steam reforming, and water gas shift.
► Coupling between the precious metal and storage components is major determining factor of the NOx conversion and product distribution.
► Models needed that explicitly account for the coupling, in order to identify improved NSR catalysts, LNT designs, and operating strategies.