NOx and soot removal over Ba- and K-based Pt/Al2O3 4-ways catalysts

Introduction The tightening of diesel emissions limits is nowadays driving research and development on control technologies for the reduction of harmful diesel exhaust emissions. The so-called 4 ways catalysts able to reduce NOx as well as CO, HC and particulate in the diesel exhaust emission are under development. Among these, the DPNR (Diesel Particulate NOx Reduction) technique, which involves the use of a lean NOx trap catalyst (e.g. PtBa/Al2O3) working under lean-rich cycling conditions, is the first commercialized example of such a technology. Further improvement of the DPNR techniques are however needed in view of enhancing the system’s efficiency to comply with future lower emission requirements. In a previous paper we have considered the reactivity of model Pt-Ba/Al2O3 and Pt-K/Al2O3 catalyst samples in the simultaneous removal of NOx and soot. Under model “clean” conditions the selected catalyst samples are able to simultaneously remove soot and NOx when operating under cycling conditions, but the K-containing sample is by far more active in the soot combustion than the Ba-based catalyst. In this work, to provide further insights on the reactivity of Pt-Ba/Al2O3 and Pt-K/Al2O3 DPNR catalysts, and on the interaction between the NOx reduction and the soot oxidation functions, the catalytic behaviour of the same Pt-Ba/Al2O3 and Pt-K/Al2O3 catalyst samples used in previous studies has been analyzed under different experimental conditions.