Supported DPNR catalysts for the simultaneous removal of NOx and diesel particulate

DPNR (Diesel Particulate‐NOx Removal) catalysts have been proposed to accomplish particulate (soot) and NOx removal from diesel exhausts. Standard DPNR catalysts consist of precious metals and alkaline/alkaline‐earth metal oxides dispersed on metal oxide supports such as alumina. In our study a homemade Pt‐Ba/Al2O3 (1/20/100 w/w) catalyst, prepared by impregnation of γ‐alumina with Pt and Ba salts, has been employed. The aim of our work was to analyze the effects of the presence of soot on the behaviour of the DPNR catalyst in terms of NOx storage/reduction and provide new insights on the role of stored NOx in the soot combustion onto the catalytic surface. For this purpose, NOx storage/reduction experiments have been performed by alternating fuel‐lean and fuel‐rich conditions (TRM, Transient Response Method) both in presence and in absence of soot. The stability/reactivity of the stored NOx and the interaction between soot and the adsorbed species have also been investigated by Temperature Programmed Methods under inert flow (TPD) or in presence of oxygen (TPO), with and without soot. All these experiments point out the complex interplay existing between soot and stored NOx. The presence of soot decreases the storage capacity of the catalyst and has a destabilizing effect on the NOx adsorbed species. There are also evidences of the stored NOx participation in soot oxidation, by direct participation of the adsorbed species and/or the release of NO2 and O2 which actively oxidize soot.