Me (Cu, Co, V)-K/Al2O3 supported catalysts for the simultaneous removal of soot and nitrogen oxides from diesel exhausts

Structured catalysts 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. Alumina suspensions were prepared using a high dispersible boehmite. Viscosity and pH of this suspension strongly depended on their composition. Highly viscous suspensions led to the formation of cracks and defects that resulted in the detachment of the catalytic layer from the walls. Textural and chemical properties of the coated monoliths were determined by means of N2-physisorption, X-ray diffraction and temperature programmed reduction. Activity of the prepared catalytic filters in the simultaneous removal of soot and nitrogen oxides was tested in a fixed bed installation in the presence of 500ppm NO and 5% O2 and at temperatures from 250 to 650°C. Almost complete oxidation of the carbon black employed as soot surrogate was measured in most cases, with NO reduction reaching 50% in the presence of the most active Co–K catalysts. Co-containing catalysts showed higher activity than Cu and V-ones. Enhanced activity can be ascribed to higher ability to generate NO2, but also to particular layer thickness and morphology which facilitate alkali mobility, key issue in the simultaneous removal mechanism. ► Me–K/Al2O3 (Me=Cu, Co, V) structured catalysts for diesel exhaust gas cleaning. ► Cordierite monoliths washcoated with alumina-suspensions. ► Simultaneous removal of soot and NOx was achieved at temperatures higher than 400°C. ► NO2 formation and subsequent reaction with soot was found to be fundamental. ► Catalytic layer morphology determines alkali mobility, key issue in simultaneous removal mechanism.