Cu-SSZ-13 as pre-turbine NOx-removal-catalyst: Impact of pressure and catalyst poisons

Abstract

The development of highly efficient engines with lower exhaust gas temperatures leads to new challenges for catalysts in the aftertreatment system. One option for overcoming this is a catalyst positioned in front of the turbocharger with an exposure to higher temperature and pressure. The impact of increased pressure and typical catalyst poisons on the catalytic performance of a state-of-the-art Cu-SSZ-13 catalyst has thus been studied during the selective catalytic reduction of NOx with NH3. Various reactions including NO/NH3 oxidation, standard and fast SCR have been tested in a temperature range of 180–600°C. Propene as representative for small hydrocarbons and SO2 have been added under reaction conditions to analyze the direct influence at relevant reaction temperatures. An increased pressure resulted in a strikingly higher DeNOx-activity especially under Standard-SCR conditions, which was mainly due to higher NO oxidation to NO2 in the gas phase and a higher residence time. Even though propene led to a temporary competition between SCR-reaction and propene oxidation, the small decrease in DeNOx-activity can be overcompensated by the higher pressure and temperature within a pre-turbine configuration with no need for regeneration steps. In contrast, SO2 caused severe deactivation at low temperature but no influence at high temperature. Reactivation was not completely possible, which suggests some highly stable sulfur species. The higher pre-turbine temperature enables an earlier regeneration, showing a further advantage of pre-Turbo-SCR.