Modeling and analysis of ammonia oxidation and nitrous oxide formation on a dual-layer ammonia slip catalyst for diesel after-treatment

A comprehensive one-dimensional kinetic model was developed to detail ammonia oxidation and nitrous oxide (N2O) formation on a dual-layer ammonia slip catalyst (ASC). The ASC kinetic model consists of Cu/SSZ-13 and Pt/Al2O3 kinetics with the overall mass transfer coefficients. The Cu/SSZ-13 kinetic includes multi-site NH3/NH4NO3 storage, NO/NH3 oxidation, SCRs and N2O formation. The N2O formation over Cu/SSZ-13 includes NH4NO3 thermal decomposition and NOx-assisted NH3 oxidation on different active sites. The Pt/Al2O3 kinetics consist of elementary reactions involving five surface species and N2O formation. The simulated results indicate that the developed model has good prediction ability for reactant conversion and product selectivity. The developed kinetic model further investigated the influences of the NO/NH3 ratio and space velocity on catalyst activity and selectivity. An appropriate NO/NH3 ratio benefits low-temperature NH3 conversion increase and N2O emission reduction. The addition of NO in the feed gas promotes the SCR reactions in the top SCR layer and reduces low-temperature NH3 oxidation into N2O in the bottom Pt/Al2O3 layer. The space velocity impacts the NH3 conversion and N2O selectivity. The increment of space velocity leads to simultaneously decreased NH3 conversion and N2O selectivity. The developed model could be used for after-treatment design and optimization of model-based control technologies in real applications.