Enhanced Selective Oxidation of NH3 in a Pt/Al2O3@CU/ZSM-5 Core Shell Catalyst

The ammonia slip catalyst (ASC) is an essential final step in the emission control system and involves the selective oxidation of NH3 to N2. The state-of-the-art ASC has a dual-layer architecture comprised of a Pt/Al2O3 (PGM) bottom layer and a metal (Fe, Cu)-exchanged zeolite (M-Z) top layer. The first part of the project deals with the challenges of reducing the PGM loading and ASC volume while enhancing low temperature activity. This is done by scaling down the dual-layer concept to the level of a single core-shell catalyst particle, Pt/Al2O3@Cu/ZSM-5, comprised of a PGM core and M-Z shell. The core-shell catalyst had an equivalent activity to that of a conventional Pt/Al2O3 catalyst containing 3-times higher Pt loading. The core-shell catalyst showed exceptional NH3 oxidation activity and N2 selectivity. The second part of the research is to investigate the NH3 oxidation kinetics over Pt/Al2O3 catalysts under atmospheric conditions for a wide range of NH3 concentration. We were able to show the non-monotonic reaction rate as a function of NH3 concentration for Pt/Al2O3 catalysts in presence of excess oxygen. We also showed the variation in reaction order from positive to negative order with zero order reaction at maximum reaction rate. Milling of Pt/Al2O3 resulted in enhanced NH3 oxidation activity. A microkinetic model with site-competition was developed which could predict the variation in reaction rate and order of the reaction. The final part of the research deals with the development of a working model for the core-shell catalyst with the microkinetics derived from the kinetic study over Pt/Al2O3 and along with multi-step SCR kinetic formulations to simulate the ASC performance of the Pt/Al2O3@Cu/ZSM-5 core-shell catalyst. Using the model we showed an optimized core-shell structure by investigating the ASC performance based on Pt loading and shell thickness. Finally, we discuss the scope of the future work based on our results and observations.Chemical and Biomolecular Engineering, Department o