On-Filter Integration of Soot Oxidation and Selective Catalytic Reduction of NOx with NH3 by Selective Two Component Catalysts

Abstract

A group of catalysts was developed with the purpose of enhancing the soot oxidation in the selective catalytic reduction on filter system, without negatively effecting the NOx conversion associated to NH3 oxidation. The impregnation with alkali metal of a series of supports, characterized by a lack of strong superficial acid sites, improved soot oxidation simultaneously preventing ammonia adsorption, thus its catalytic oxidation. Strong synergy was observed between a ZrO2–CeO2 support and potassium, decreasing the T50 of the soot conversion of 170 °C in loose contact. This catalyst was added to a Fe-ZSM5 selective catalytic reduction (SCR) catalyst without negative effect for the SCR activity. The complex interaction between the potassium-based soot oxidation catalyst and the SCR one was investigated. The soot–soot oxidation catalyst-SCR catalyst contact mode was found to be a key factor and the increased contact of the soot–soot oxidation catalyst is preferable. Such dual component catalyst system was demonstrated to be promising for simultaneous removal of NOx and soot on a single filter.