Catalysis in Diesel engine NOx aftertreatment: a review

The catalytic reduction of nitrogen oxides (NOx ) under lean-burn conditions represents an important target in catalysis research. The most relevant catalytic NOx abatement systems for Diesel engine vehicles are summarized in this short review, with focus on the main catalytic aspects and materials. Five aftertreatment technologies for Diesel NOx are reviewed: (i) direct catalytic decomposition; (ii) catalytic reduction; (iii) NOx traps; (iv) plasma-assisted abatement; and (v) NOx reduction combined with soot combustion. The different factors that can affect catalytic activity are addressed for each approach (e.g. promoting or poisoning elements, operating conditions, etc.). In the field of catalytic strategies, the simultaneous removal of soot and NOx using multifunctional catalysts, is at present one of the most interesting challenges for the automotive industry.