Catalytic filters for the simultaneous removal of soot and NOx: Influence of the alumina precursor on monolith washcoating and catalytic activity

Different highly dispersible boehmites were used as alumina precursors in the preparation of washcoating suspensions for the preparation of catalytic filters containing Cu or Co together with K as the active phase. Catalysts were characterized by means of SEM microscopy and N2 adsorption, in order to determine their morphological and textural properties. Their activity in the simultaneous removal of soot and NO was assayed in a fixed-bed laboratory installation. Morphology of the deposited layer was found to strongly depend on the type of precursor used in the preparation of the washcoating suspension. Textural properties varied as well when employing the different precursors. In fact, the textural properties of the catalytic filters determined their activity, concretely towards NO reduction. Co-containing catalysts were found to be more active in general than Cu-loaded ones, particularly towards the elimination of NOx. The catalysts prepared were able to selectively reduce NO at temperatures between 475 and 575 °C, by means of a simultaneous elimination mechanism taking place in the presence of the carbon material. Soot oxidation was found to be complete in most cases, and almost totally selective towards CO2.