Design of Dual Layer Catalysts for NH3 Oxidation in Automotive Exhaust

摘要

Introduction Automotive catalysts for selective catalytic reduction (SCR) of NOx by NH3 frequently are equipped with a short zone of an NH3 oxidation catalyst. The purpose of this so called NH3 slip catalyst is to allow a more aggressive dosing of NH3 without increased NH3 emissions. It has been recently proposed that the selectivity of the NH3 slip catalyst can be improved by a bi-functional dual layer catalyst. The lower layer contains a platinum catalyst which oxidizes NH3 to N2, N2O and NO. The upper layer contains an SCR catalyst which removes some of the NO formed in the lower layer by reaction with NH3. In this way the upper layer improves the N2-selectivity of the catalyst. The purpose of this contribution is to show that numerical simulation is a useful tool for the design and optimization of such multi-layer catalyst architectures. The simulation results will also be compared to experimental data on the double-layer NH3 slip catalyst.