Dual-Layer Ammonia Slip Catalysts for Automotive SCR Exhaust Gas Aftertreatment: An Experimental and Modeling Study

摘要

To reduce NO_x emissions from lean exhaust gas (e.g., Diesel exhausts) selective catalytic reduction by NH3 (NH3-SCR) has become an established process for passenger cars as well as for heavy duty vehicles [1]. The reducing agent, NH3, is adsorbed onto the SCR and then consumed by NO_x reduction reactions. The amount of ammonia fed to the reactor must be controlled depending on the operating conditions in order to maintain a high level of NH3 adsorption and NO_x conversion of the SCR on the one hand. On the other hand, NH3 emissions from the aftertreatment system into the environment are not desired and have to be avoided. In order to reduce as much as possible the amount of released ammonia, the addition of another catalytic device downstream the SCR one can be an efficient and reliable solution. Furthermore, to maintain the system as compact as possible, one solution is to add an ammonia oxidation functionality directly in the rear part of an SCR monolith (Fig. 18.1a). In this way, an NH3 slip catalyst (ASC) is added after the SCR to oxidize NH3 leaving the SCR brick [2].