Kinetic Monte Carlo Simulations of Low‐temperature NH3‐SCR over Cu‐exchanged Chabazite

Abstract

Cu‐exchanged chabazite (Cu‐CHA) is widely applied for ammonia assisted selective catalytic reduction of nitrogen oxides (NH3‐SCR). The Cu+ ions are at low temperatures solvated by NH3 forming mobile [Cu(NH3)2]+ complexes. The dynamic behaviour of the complexes is critical as O2 adsorption requires a pair of complexes to form a [Cu2(NH3)4O2]2+ peroxo‐species over which NO couples with NH3. Here we introduce a first principles‐based kinetic Monte Carlo approach to explore the effect of the Al‐distribution on the reaction kinetics of NH3‐SCR over Cu‐CHA. The method allows us to scrutinize the interplay between the pairing of [Cu(NH3)2]+ complexes and the reaction landscape for the NH3‐SCR reaction over the peroxo‐complex. The Al‐distribution affects the stability of the [Cu(NH3)2]+ pairs as well as the kinetic parameters of the SCR‐reaction. The turn‐over frequency is determined by the stability of the [Cu(NH3)2]+ pairs and the relative strength of NO and NH3 adsorption once a pair is present. The results establish the hierarchy of effects that influences the performance of Cu‐CHA over NH3‐SCR and provide a computational basis for further development of the Cu‐CHA material.