PNNL

Abstract

The control of NOx (NO and NO2) emissions from combustion processes, including vehicle engines, remains a challenge particularly for systems operating at high air-to-fuel ratios (so-called ‘lean’ combustion). The current “3-way”, precious metal-based catalytic converters are unable to selectively reduce NOx with reductants (e.g., CO and residual unburned hydrocarbon) in the presence of excess O2. In the last few years, worldwide environmental regulations regarding NOx emissions from diesel engines (inherently operated ‘lean’) have become significantly more stringent resulting in considerable research efforts to reduce NOx under the highly oxidizing engine operation conditions. Urea selective catalytic reduction (SCR) and non-thermal plasma assisted NOx reduction have been explored as possible technologies. In recent years, alkaline and alkaline earth oxide-based NOx storage/reduction catalysts (especially BaO/Al2O3) have been developed, and have shown promising activities for lean-NOx reduction [1,2].