Catalytic filters for the simultaneous removal of soot and NOx: Effect of CO2 and steam on the exhaust gas of diesel engines

Catalytic filters for the simultaneous removal of soot and nitrogen oxides were prepared by means of coating cordierite monoliths with alumina-based suspensions containing Cu, Co or V and K as the catalytically active phase. Textural and chemical properties of the coated monoliths were determined by means of N2-physisorption, XRD, SEM-EDX and temperature programmed reduction. Activity of the catalytic filters in the simultaneous removal of soot and nitrogen oxides was tested in a fixed bed installation in absence and in presence of steam and CO2. Complete soot oxidation was measured for some of the assayed catalytic filters, with high selectivity to CO2 formation. NO reduction was preceded by a peak of NO2 formation, which corresponded to maximum soot oxidation rate, pointing to the formation of NO2 as a key step in the reaction mechanism for the simultaneous removal. Presence of steam and CO2 diminished catalytic activity and selectivity for soot oxidation.